You don't know what you've been missing. All three are excellent, and IMO the best reasons to own a PS2. Choice between GTA and R&C, and I'll go with the Lombax and Robot.
Imagine if Mario 64 stared a Lombax, was linear and not about collecting stars, but about collecting usable weapons. Now imagine that it had a humorous Sci-Fi story, litereally thousands of things to blow up, and suberb voiceovers. The first game is more about exploration for the first half, and the second half is a lot about shooting stuff. The second one is almost strait-up action with occasional platforming, and UYA is basically more of the same.