I haven’t read everyone’s responses here, so my apologies if I’m covering turf that’s already been covered. But:
As somebody who owns… almost every, if not every “Big Space Game” (Star Trek Ascendancy, Forbidden Stars, Outer Rim, Xia, Space Empires 4X, Red Alert, Dune, Rex, Dune Imperium, Empires of the Void I and II, Eclipse, Eclipse 2nd Dawn, Twilight Imperium 1st-4th Edition, etc…) and many of the smaller space games (Quantum, Ascending Empires, Talon, Android, Ironclad, Space Hulk, etc…), I have thoughts. And the first of which is that my thoughts aren’t probably that useful, since I love this genre with the passion of a thousand suns.
That’s not to say I own everything. It’s impossible unless you have infinite money, and even then you wouldn’t have time to play all of them.
That stated, Eclipse is pretty good. I found it disappointing compared to TI3, which was its contemporary at the time, but it did a few things better than TI3 (tech trees, in particular, and exploration, which TI3 had a module to do but it was clunky and not particularly satisfying). And then TI4 came out and it was everything I wanted (and continue to want) in a space-opera-in-a-box.
Xia is a sandbox game, and a pretty good one at that. The exploration elements are very swingy, but the game itself is pretty good aside from a few key problems (the big one is the runaway-winner issue, where it can be very, very difficult to pull up after one player starts doing really well… the easy solution to that is that if you’re getting your teeth kicked in, maybe it’s time to call it). I also don’t like that not all paths to victory are equally viable in each game (the Merchant method relies really, really heavily on finding the right planets and/or resource fields early), and there is a lot of fiddly steps between each turn (worse with higher player counts, since there is always
The Pirate, The Merchant, and The Cops that have to be activated and moved, plus some board elements).
Now, I own, but haven’t played Eclipse 2nd, but I suspect it will be pretty good at the same things the original did well (exploration, neutral enemies you can beat up, interesting asymmetric races that aren’t a pain to learn, and of course that gorgeous/brilliant tech tree/ship upgrade system) and struggle in the same places as well (no meaningful diplomacy or trade, and player elimination being a very real, very present threat). I also expect TI4 will continue to be better with 3-6 players and Eclipse 2nd will probably be better with 2, but I doubt I would ever personally play Eclipse with 2… and I think Star Trek Ascendancy does exploration way, way better than Eclipse, which is a statement of some weight since Eclipse does exploration really well.
As for Xia, I like it, although it is swingy and relies on dice a bit too much for my tastes (and I’m always skeptical about a game where it sometimes makes more sense to suicide yourself to get back to a planet with a new ship rather than limp back because you ran out of fuel/power). I think Outer Rim has much stronger narrative chops, but it’s also much, much more “on rails” than Xia (there are literally only 2 paths through the galaxy), but it also hands NPC/neutral factions much better.
Oh, as an aside: Space Empires 4X is great as a wargame with 4X elements, and Forbidden Stars is really a knife-fight-in-a-phone-booth, but both work very well with 2 players, but the focus is on the combat, as opposed to the other 3X-options. Talon if you want a straight-up-fleet battle is good, Red Alert is great and clean and fast, and Quantum or Ascending Empires if you want your space game to be silly rather than strategic are both really solid.
I do not know if that helps or not!