I've only played the newest one (Crack in Time), which was pretty awesome. Loved the hilarious cut scenes, and the levels with Clank in the Great Clock. Only made it about halfway through before I got bored and moved onto something else. Think I wasted too much time trying to collect items on all the little moons and side missions. Should have just barreled through the main story to see how it unfolds. Still plan to beat it eventually though.
The new one that's coming out (R&C: All 4 One) looks pretty cool too. It's gonna be four player co-op like in New Super Mario Bros.