Ratchet: Deadlocked comes to mind. While still a hilarious game, its tone is still very different overall to the rest of the series. It's even the 4th entry to match Tekken 4.
Unlike Tekken 4, however, Deadlocked is actually good. Really good.
That's actually a good comparison.
And yeah, Ratchet Gladiator is one of my favourites of all time.