I've always liked the Armored Core series in concept: completely customizing your own mech and then using it in battle has a certain appeal, but the games themselves always came up a little bit short. The controls never felt very good and the mech were all slow and ponderous without emparting the feel of power that the more "realistic" mech games, like Mech Warrior and Steel Battalion have. Armored Core 4 seems to have addressed most of these issues: the controls feel much more responsive and the mechs are likewise much faster and more nimble. There are still a few issues: the lock on can't track enemies beyond your field of view, so its usefulness is severely limited, this is exacerbated by the fact that the mechs turn extremely slowly. Still, I had a lot more fun with this than with some of the previous incarnations, which is certainly a step in the right direction.
Simulation/Giant Robot Simulation