This game is all the way up there with classics like Heroes III and Master of Magic. Games that great are hard to rank but after more than a decade of playing them Age of Wonders has surpassed them both in my opinion. The game is more than any other the spiritual successor to Master of Magic and combines a magical atmosphere with loving attention to detail and unparallelled strategic depth. The only part of the game that doesn't stand the test of time too well is the artificial intelligence which is very poor. However on the high difficulties there is still plenty of challenge to be had. I should also mention that the game still has a dedicated community at Heavengames (which I'm apparently not allowed to link to). And a final thing. The automated play by email functionality doesn't work properly any more. Luckily there is an easy to use fan made alternative available at heavengames. Playing AoW by email is a real treat and highly recommended.
I approached Galactic Civilizations looking for something new after having recently played a lot of Master of Orion 2. Having played GC for a few days it seems to me that it has much in common with MoO2 but that it is much more cumbersome and has a much less intuitive interface. I could look past that if GC offered greater strategic depth than MoO2 but I don't think that's the case. I may be mistaken about both the interface and the depth since I have only played the game for a few days. Maybe the true strength of GC only reveals itself after some time. But I don't think I have the patience to find out. Also the lack of multiplayer support is a big minus. In conclusion GC seems like a good game but just not good enough to compete with the many alternatives in the genre.