I really can't recommend any other 4xs, really. I played the Total War series for a long time, then gave up in disgust as the suck factor was introduced with Rome and started to increase exponentially with its expansion. I've tried a few others, but nothing so far has held my attention like GCII. I started as a board gamer (OGRE, Third Reich, War and Peace, World in Flames, Swords and Sorcery, etc.), with only human opponents available, and I think that soured me on most of what's out there in terms of AI opponents today.
I recently posted part of my early game strategy
here (look for my first post in the thread). The only thing I would add is this - put some ability or political party points into Diplomacy, as well. Diplomacy not only helps you trade techs, it also improves your relations with other races, making it less likely that they will declare war on you. It's always best to wait until you're ready to go to war, after all.