The main issue of X-Com:EU is that it was mainly designed as a simple video console game with simplified controls for simple people.
It has some good features, like the class traits (e.g. medics with their stabilization and revival) and nicely designed maps, but I prefer more flexibility on the battlefield (TU system, no alien spawn-ganging) and the geoscape (more bases, more aircrafts, random UFO encounters including own base attacks) what Xenonauts offers. Games should offer more than fancy graphics and repetitive cinematics: complexity.