I had a really good post all written up, and hit backspace and stupid Firefox deleted everything...
I hope it was about Ryzom or any other MMO than EVE.
The general spin of my post was that I think "complexity" as I understand it in games comes from "having many different things to do" other than killing, or looting, or "getting teh xp". Not just that you can, because you're not restricted (like in the latter game, that I won't mention) but because it is an integral, designed part of the game.
Then I said for example, Wurm was pretty complex, but suffered from crappy graphics, bugs, a horrible horrible painful interface, and a total absence of fun (not Fun... it had plenty of Fun, but it wasn't any fun). And then I mentioned other game, which I forgot right now.
Basically, elements like crafting (but not everybody making the same Legendary Vibranium Sword of Underpant Disintegration +12 from one of those darned "recipes"), interesting building (City of Heroes, for example, let's you make a decently different Headquarters/Base/wossname) make a game complex IMO. Having a really complex formula dealing with imaginary numbers for calculating hit rolls is not complexity to me, in game design terms.
Just clearing that out, in case my definition of "complex" is not the same as the rest of the posters in this thread.