Hi,
System Requirements: GC2 wins big. I bought my laptop in 2003 and cannot play C4 on it. There's no reason for this, other than bloat.
Graphics: C4 wins big. When playing GC2, I have to zoom out so that I don't get the wonderful graphics, because I find it hard to tell anything apart. The crummy icons are much easier to disambiguate at a glace than the glitzy graphics. I find it hard to tell ships apart, even one race from the next. Planets too. C4's graphics are pretty, yet I immediately know what everything is.
UI: C4 wins big. GC2 has a wretched UI. C4 is hardly marvelous, but in this contest it doesn't need to be.
Support: Tie. Both companies release patches that actually improve the game. Stardock calls these things "bonus packs," as though fixing bugs is above and beyond the call of duty. Orwellian marketing hype aside, the developers of both games fix bugs and tweak the game based upon user feedback.
Genre: N/A. Both are turn-based "4x games," but different. If you like spaceships, C4 won't do much for you. If you don't....
Compared to best in genre: C4 wins. I consider MOO2 to be the best interstellar game, and GC2 simply isn't as good. GC2 has more micromanagement, less effective graphics, less atmophere, less strategic variability - -every race plays differently (though GC2 does have some interesting stuff going on), and I'm not even sure the AI is better, in terms of the challenge it poses. I find C4 to be better than C3, and perhaps better even than C2.
Micromanagement: C4 wins slightly. Ironically, this is because of the centralized economy screen in GC2, which demands tweaking every turn, based on the production of an increasing number of planets. It does not help at all that each planet can have a focus. It helps even less that the economy sliders don't always slide, and don't always slide in the expected direction. Populations caps and morale also need watching. C4 isn't great in this regard; population growth is not always allocated as expected. Still, the production queues and especially the use of production overflow goes a long way toward reducing the necessary umanagement and its attendant frustration.
Unit design: GC2 wins big. You simply cannot design units in C4, and their use in combination is relatively simple. However, the GC2 AI isn't very good at unit design or combining them effectively.
AI: C4 wins. I find the C4 AI to be quite challenging on its default level. It has flaws, and cannot learn to correct them, but does not tend to make Big Blunders. I play the GC2 AI on Tough, and from my very first game outdid it in everything every time. The AIs cannot even seem to manage their economy, which always tanks early into the game. The equivalent level in C4, where the AI is on equal terms with the human player, really is a challenge.
Tech Tree: C4 wins. The GC2 tech tree is staid and uninspiring. The C4 tech tree offers more choices that have strategic impact.
Diplomacy: C4 wins. The AIs in GC2 do some very strange things. The C4 AIs are less strange, and much smarter.
Empire Development: C4 wins. The terrain in C4 is far more varied than in GC2. The things one can do with terrain is also more varied, as are the strategic choices. Both games have essentially the same basic resources: Food, industry and commerce/economy, but use them in different ways. There are more ways to get these resources in C4 than GC2. Expansion is a no-brainer in GC2, even in 1.1; C4 expansion requires more thought: It is easy to lose the game by overextending.
Trade: GC2 wins. Sending out freighters is an important strategic element in GC2. C4 trade just happens. Civic choices affect this, but less thinking is required.
Victory options: C4 wins. Culture victories in C4 are hard, while influence victories in GC2 are too easy. Conquest is, well, conquest. When a human player is ready to steamroll, no AI can really stop it. Getting there in C4 is harder, however.
Racial options: C4 wins. GC2 races have more variability, but C4 races have more interesting variables! The civ unique unit and two leader traits can utterly change the way the entire game is played, from civ to civ.
Governments/Civics: C4 wins big. C4 has five civics, and five choices in each. No single combination is best; the choice depends on strategy.
Music: C4. Great music for most epochs! Not original, but who cares?
Replayability: I don't know. I stopped playing C4 after playing a game as Rome and finding that my Praetorians were just *too* awesome. But after playing GC2 for a while, and comparing the strategy discussions on the two sets of boards, I'm beginning to think that C4 is a much deeper game. I intend to install the latest patch and find out. Alas, unlike GC2, C4 will not run on my laptop.
Anyway,
Ken