Having played both XCOM:EU and the last build of Xenonaughts that they released, the differences are big but they don't cause one game to "win" over the other.
From the look and feel of it Xenonaughts is going to be a much truer remake of the original X-Com, both in look and feel. However, I'm not going to judge it as an "amazing remake" until it's out (I still preordered though). I still remember how UFO: Extraterrestrials turned out at the end.
In sharp contrast to Xenonaughts, XCOM is an action game. It's fast, smooth and a bit more action-y. The research and engineering systems are toned down to speed things up, but still interesting and they provide a certain necessary amount of X-Com flavor to the game. Combat is the same way. Soldier classes, inventory and the like are all toned down in their complexity. Is that a bad thing? No. It's not a great throwback to X-Com, but they work great for the way that combat now works in XCOM.
My only real complaint about XCOM is that it's less aimed at the long, marathon style games I loved when playing X-Com. A result of this is that ufo interceptions are fewer and abduction missions are more aimed at balancing terror levels across the world. Both of those can be (and have been) modded to shift them back to the old school values.
I'm glad I bought XCOM and I'll enjoy it for a long time now. But its different enough from the old X-Com style of gameplay that I'm still awaiting the release of Xenonaughts with great anticipation.
