I love the part that for three whole games, Ratchet has struggled with fame and recognition, and when Vox offers him all the popularity and merchandise he'd ever wanted, he refuses without a second thought. Ratchet grew so much since he started out...
Reducing the weapon count was one of the best things the game did. Every gun is useful and means something, plus, as you said, the mods are so good and really allow for a personal armoury.
No comment on the Co-Op? Start a session with a friend in the morning, Exterminator difficulty and play trough the game packed with non stop action. It's old school splitscreen and it's mad fun. I don't know how often I played this game with a friend and we just had massive fun playing trough it.