Well, though I own GalCiv 2 I don't get to play it very much. I think the main fundamental difference is that in GalCiv 2 you do actually get to design your own ships. You research various weapons and components, and while there are some premade ships, a lot of the fun is in putting together your very own. The designer is pretty awesome, actually - ship parts have points where you can attach other parts to, so you grab a hull and depending on its size you can have practically hundreds of little points to attach other components to. There are lots and lots of "decoration" type components that you can attach (and resize so they look fitting) on top of the standard weapons/sensors/life support/engines/armor/shields to basically create the Ship of Dreams.

I'd say that's really the biggest feature that stands out.

GalCiv2 doesn't have online multiplayer. 

+ You play against the AI in the campaign.   Each expansion pack also has a campaign.

+ You can play custom game against any number of AI opponents and a bunch of other settings you can tweak.

+ You can also play a "metaverse" game which is basically a single player game where you finish it and then post your score to an online leaderboard.  There are a ton of people on the galciv2.com forums that are really into it.  There are even Metaverse Leagues where the scores you post are part of a team leaderboard effort.

I like GalCiv II way more than Civ4. The setting in space is just much cooler. I do not like the comic style of Civ4.

Besides these issues of taste - GalCiv II is another game than Civ4. Maybe the basic system is in parallel, but you cannot compare them i think. And i believe GCII is more complex. It may be because i spent much more time with GCII and it reveals more and more of its tactical complexity when you get deeper into it. Just give it a try, at least the demo. If you are into 4X strategy GCII definitely shouldnt be missed. It is one of the best, for sure.

You kidding me!? Gal Civ 2 Twilight is one of the best if not THE best turn strategy game or for that matter strategy game out there, is not just Civ4 in space is waaaaaaaaaay better and I agree i own all three Civ4, Sins and Gal Civ2 and last time I checked the only one that kept me playing 6 months straight (and I mean straight i didnt played anything else and spent 2-10 hours playing) every day of the week.

There's undoubtedly great replayability in GCII. The ship designer is certainly one of its major advantages, but there's also great depth in strategy and game mechanisc- especially in the second expansion, where every civ gets its own tech tree, bonuses and can use its own strategies. The AI is pretty impressive too, at least on higher levels.

Some players, however, may be put off by the simplicity of battle mechanics: It's resolved in auto, and the most powerful fleet (in terms of attack vs. defence points) wins. There are many factors influencing that, though, with military starbases or special fleet-wide bonuses applied by 'command vessels' in the fleet (a recent addition in Twilight of the Arnor), and also one can always get the strategic advantage by investing in research of a different kind of weapon (beams, missiles or mass drivers) that the opponent has no defences for. So many strategic options are indeed possible, if not on the level you would find in MOO or Space Empires.

If GalCiv had that kind of battle complexity too, it would be one of the best 4X games ever. No, strike that- It is one of the best already; it would become THE best.

Galciv is the only space strategy game I have ever played. I am more of a Fantasy player myself.

However once I tried galciv2 I was hooked. There is just so many different possib ilities when playing that game that's it's way out there.

You can play with as many opponenets as you want in a univers as big as you want. You can try and be a xenophobe species or the biggest merchant in the univers. You can be a manipulator and pull the strings from behind, or you can be a tyrant and kill everybody. You can have anykind of strategy game with Galciv. IT'S  NOT A SPACE SIMULATION GAME and it's NOT A COMBAT SIMULATOR. battle are resolved by the AI but everything else you have a control over.

I enjoy it very much. it's never boring once you find the exact difficulty level you need. There is like 10 different difficulty levels so it can be perfectely tuned to the user. That is hot. The AI is very very good. The ebst I've ever played.

I suggest you try it! You won't be sorry.

Just dont expect too much from the tutorials - they cant give you more than a basic instruction. It is normal to be a bit overwhelmed but once you managed the learning curve it becomes rewarded by a truly great game. I am not a big gamer anymore but this game somehow managed to suck me in again and letting me spend whole days with playing. Which proves to me that graphics almost dont matter in terms of fun, in GalCiv you get offered a good looking game too if you want to zoom in, but i spent most of the time in the tactical map wondering how moving symbols can be that addicting. It really is a great piece of game design.

So welcome to the world of addicts where the basic sentence in your life will be "Just one more turn..."

Opinions and taste are subjective, but here is mine: As good as GCII--ToA is (and it is very, very good), it still can't hold a candle to CivIV. YMMV depending on your tastes. First, I invariably play a turtle/development oriented strategy in TBS games. This is just way more interesting in CivIV since you have a whole lot more development tools at hand. Not only is the entire workers/city resources concept absent from GCII, but the number of city (or planet) developments  is limited by PQ. That is a very viable gameplay concept to enforce choices, but to a development oriented player, it is just way less fun than CivIV. Second, the CivIV UI is just much better. Plus CivIV is a much more transparent game. Documentation (by which I mean both manuals and ingame info such as rollovers) has always been Stardock's most obvious weakness. Through the Civilopedia (a feature GCII has always badly needed) and rollovers, information on just about everything is at your fingertips in CivIV. You can calculate, to a couple of decimal places, exactly what the effect of building a city improvement will be. You can't do that in GCII (or at least I have never been able to in several years of trying). This lack of transparancy in GCII has always been my biggest frustration with the game.

I also admit that designing units, which most consider a major strength of GCII, is actually a negative for me. Although I thrive on micromanagement (governors and automated workers are a heresy to me) this concept just leaves me cold and represents unwanted work. I largely felt the same way about unit design when Firaxis used it in the classic Alpha Centauri. (I recognize I was in the minority in both games.) Finally, and this is getting even more subjective, I find GCII (and space 4x games generally) to be a bit abstract. Stardock has done a great job with GCII's graphics, but they are less involving to me than the real world geography of Civ. (Which is a bit ironic since I have been a SF fan for decades.) Nor does building bigger starships provide me with the same satisfaction of  moving my primitive civ through the bronze age, the Renaissance, and the Space Age.