I've been playing the Milestone builds, and of course I'd played a fair bit of earlier builds, but the Milestone builds do feel much more mature and are also the first time I've gotten past the early midgame, so it seems like a good time to provide some renewed feedback. I've seen a lot of what others have posted, so I'll omit points that have already been brought up many times unless I have additional insights to share. Mostly staying away from balance, too.
All in all, well, I can't stop playing in the evenings and I'm particularly impressed with how much gameplay has improved over X1 thanks to mostly small changes.
People have said the Cleaner arc is short, and after reading those comments, I understand. They featured more prominently in earlier builds but aren't so visible in the EA build after all. Design-wise, getting rid of the mandatory Cleaner base attack was the right choice, but it can lead to the Cleaners coming out of nowhere seemingly. You attack the Intel Hub without a good background on who they are and then most of their story comes after you eliminate the organisation entirely.
I strongly suspect the flow of the Cleaner story can be improved with some fairly minor changes. They should appear in the first mission (the alien research site) alongside aliens. This will create a memorable moment for the player (who are these secret service type guys? why are they attacking me, are they with the aliens?) and provide an opportunity for the appropriate research text to show up early, giving some background. Then the player would be going into the Intel Hub to face a familiar enemy. Especially recovering a Cleaner body from the first mission would make a difference. As things are now, you're almost certain to only get the Cleaner autopsy done after destroying their HQ, because the Intel Hub and the Cells end with you escaping, so you don't recover any bodies unless you drag them yourself.
A lot has been said about the difficulty of Cleaner Cells, to the point where it seems a couple negative Steam reviews appeared in frustration at the missions. These two missions aren't unfair to experienced players but they do show up fairly early and can feel unfair to new players. It's pretty undeniable that there is a difficulty spike. The Cells are harder than the Intel Hub or HQ missions, and they're harder than crash sites or even terror missions in that phase of the game. While there's been some focus on the timed reinforcement aspect, I'm not so sure that is the main problem, though of course adjusting reinforcements/timers per difficulty is a good idea.
Much of the difficulty of the Cells seems to stem from a high initial enemy count. The Cell Cleaners are tougher than most other enemies in this phase, they have burst weapons and either decent damage or good armour. Removing even one Cleaner from the initial map would go a long way - the Cells don't need radical changes as much as they need fine tuning. The other difficulty component is that you need to locate the VIP. Which is a bit weird with metagaming effects. The first time you play, you need to spread out a bit and look for the VIP. The second time you play, you know where the VIP is so you can follow the optimal tactic of heading straight for the main building, blowing open walls and finishing the VIP off with a MARS rocket salvo or something similarly explosive.
In the Cleaner HQ, the objective area should display what boosts you're getting from killing the cells, like "Cleaner Cell destroyed - defender armour weakened". This is as a reminder and as a confirmation to the player of what specifically has been accomplished.
Since air combat is going to get another pass, I'm not going to go into the actual combat mechanics now but rather some adjacent points.
There's a strange metagaming issue with damaged UFOs, which X1 also has. During a UFO wave, as UFOs go in and out of radar range, I can remember if I e.g. destroyed a particular UFO's armour if I remember the ID. I torpedoed UFO-5 so it has no armour any longer? Okay, then the next time I get a contact, I'll know if it's the same one by checking if it's UFO-5 or UFO-6. But it's unclear if I'm supposed to do this. Same issue with UFO types really, if I engaged it and know it's a Destroyer, subsequent clicks will still say Unknown. One fairly straightforward solution could be to remember which UFOs have been engaged by a squadron and, for any such UFO, show its type and perhaps damage status.
I can't help but feel that the existence of the Dynamic UFO HP option is weird and suggests an issue. It's very strange for the same UFO to get weaker or tougher depending on how many planes I engage with. No idea what to do with this, but my intuition is that the best balancing tool is fuel. If you're sending three planes where one would do, in theory you should be wasting fuel and thus be in a worse position to respond to a subsequent threat. And related to dynamic HP, I've complained before that the auto-healing of UFOs is very much a black box. Maybe the mechanic has its place but it needs to be more clear.
Compared to X1, there's the excellent move of making UFOs occasionally slow down so that it's possible to catch a faster UFO with a slower plane if you get lucky. This makes another mechanic from X1 appear awkward - if your squadron runs out of fuel, they have to go back to base, but they're limited to the lowest-fuel plane. In X1, I didn't mind, but in X2 it really feels like it'd make sense to split squadrons in-flight in such a situation, with e.g. Angels returning to base and Phantoms continuing.
Bases and Teching
There are a few surprising moments in the tech tree. One example is, if you skip Accelerated Cannon (engineer build) for planes, and go for the much superior Laser Lance, when eventually research Heavy Gauss, you'll see the engineering project to build the Gauss Cannon (whatever it was called) and suddenly discover it needs Accelerated Cannons first. This is surprising because of the inconsistency, normally each weapon tier is independent and also thematically we're building a new type of gun, not upgrading the previous one.
Starting a new base, you can assign buildings to be constructed before the access lift is complete. That is a good change but it's not even hinted at anywhere, you have to discover it by accident.
The Training Center, along with the whole training mechanic, is too much of a black box. I do see the training capacity but that's all. How fast are my soldiers getting attribute progress? How much has training contributed overall? Which attributes? Are all my soldiers training? I did not find anywhere to see those.
Base upgrades (Alenium generators, Quantum labs, etc) may be easy to miss for players who don't expect those. Perhaps a tooltip in the main base view if an upgrade is available? Hover over a generator and it might say "Alenium Generator upgrade available in the Workshop".
I find base storage confusing right now. Why are mission items not sold automatically? Not sure if there's still a reason for this. There was in earlier builds but now, unless I'm mistaken, there is no reason ever to hold on to an item you got from a mission. Research unlocks automatically when relevant and items are never used in manufacture. Then the only thing storage adds is confusion potential, exemplified by how "when can I sell Cleaner Data?" is one of the most common progression questions.
Ground combat, the meat of the game, is of course excellent overall, with significant improvements compared to just a few months ago. I really like the various alien abilities, they feel like a successful return to classic X-Com style, which is probably the main reason combat feels better than earlier this year.
A strange thing I noticed is that terror missions feel a lot easier in X2. In X1, I'd always be afraid of them, they were, well, a terror. Just like in the original game. X2 terror missions are easy but I cannot quite figure out why, they're mechanically the same as X1 after all. Some contributing factors could be that aliens always prioritise civilians (making civilians powerful meat shields), that Reaper AI in particular is dumb (they're not sneaky and so are easier to deal with) and that the terror maps have many explosive props (if a gas station shows up, that's almost cheating, a well-placed shot blows the entire area up).
Base defence missions are always a highlight for me. Some AI issues clearly present but very good stuff overall, though they could be improved by having a few more interactive props. It's a Xenonaut base, it is the perfect place for that. An explosive gas balloon in the workshop, some equipment in the lab that explodes with EMP damage, a container that starts leaking smoke if damaged in the storage room. The fights would feel more epic plus interactive props are always fun. Also, the Access Lift tile is very uninteresting. Aliens aren't coming from it anyway so ideally I'd give it a complete makeover with a rename to Command Center, but the existing tile could be improved by at adding some sandbags to hide behind.
Stun damage is difficult to balance but it's currently not there. I've repeatedly knocked enemies out without meaning to. The general rule that stun bar above HP bar means unconscious is good but some tweaks are needed. One idea is to require an actor to have just received stun damaged to fall unconscious, and disallow unconsciousness on HP damage. This is to prevent a situation where you shoot an alien, not dealing enough damage to kill but enough to knock them out. Being knocked out from a shotgun to the face is weird. Related to stun, stun guns need a clearer role. They're currently fully useless.
Tutorial tooltips - the overdamage explanation seems to pop up the first time an actor dies via overdamage, which is very likely to be a civilian from alien fire. Should probably be only if you kill via overdamage instead. Yes I tried the tutorial mode.
Tutorial tooltips - I cannot figure out what triggers the "adjacent soldiers can open doors" explanation but I got it during the alien turn and that probably shouldn't happen.
We need soldier flags back on the UI!
Servitors are mostly referred to as gun drones, except the initial research text.
Missions with reinforcements could really use a visible timer, like the abduction missions have.
Soldiers can path through burning tiles and even kill themselves by doing so.
A corner case with laser machine guns. If I fire a 10-round burst and a 3-round burst, that takes my ammo down to 7/30. Then the game won't let me fire a 10-round burst because there's not enough ammo. Makes some sense but I'd prefer to be able to force-fire anyway if I use ctrl.
Using a medkit can cause reaction fire, it should probably be exempt.
It's highly counterintuitive that winning a terror mission doesn't reduce panic in the region.