Size Matters is very good for what it is. It looks and feels like Ratchet, but it's quite short. Still fun if you're a fan though.
Secret Agent Clank is way better. Lots more content, fun little stealth elements. It's basically just another Ratchet game, but it does a very good job with it. Highly underrated game.
I'd say Tools of Destruction is up there with Going Commando as my favorite. Lots and lots of content, a good balance of platforming and shooting. I feel other entries, starting with Up Your Arsenal, suffered from less focus on platforming and more on shooting, but I've got plenty of shooters to play. I want more platformers.
Quest for Booty is a short budget title that was basically standalone DLC. If you like Tools of Destruction, it's more of that, but only a tiny bit more.
A Crack in Time is the only full game since, other than the remake, and it's very good. I don't know if I'd put it as high as Tools of Destruction or any of the first three, but it's certainly close. Also, the Clank gameplay in this is fantastic. Best in the series by far, and I wish I could play a full game of it.
All 4 One is a multiplayer spinoff that's fun for what it is, but don't go in expecting something like the main entries. When you play single player it does play a bit more like the main games, but it's still shorter and much more shallow, to allow for the multiplayer shit.
Full Frontal Assault is a tower defense spinoff. It was also a budget title sold for like $15. Good for what it is. If you like Deadlocked, it plays a lot like that, Ratchet without the platforming. Also if you got the PS3 version it came with the Vita version for free, along with Quest for Booty and Deadlocked HD for PS3. Those alone make it worth the price, assuming you don't have the originals.
Into the Nexus was once again a budget title, but they went all out with this. Despite being sold for cheap on release, it is way, way longer than Quest for Booty. Much longer than most indieshit I've played that tries to be like these games. Felt pretty much like a full game that was just a little short, rather than a budget game that was very long. The gameplay isn't stunted at all, and what you get is some of the best stuff in the series. It was the final release before the reboot, so I think they went all out. The ending is a nice ending to the whole franchise. Definitely a must play if you're a fan.
The remake is at least actually a remake, it is a new game, and not a remaster, but while some levels are completely redesigned, and there's a few brand new levels, a lot of levels are just exact replicas of the originals. Also, not every level from the original game made it into this one, and the new ones that are there aren't as good. Remember that hard as shit, very varied return to Veldin? How hard it was to finally reach the boss? Well that's all gone now, and now you just walk down some hallways and shoot guys, with no platforming whatsoever. Still one of the more fun games I've played in years, but that says more about how vidya sucks now, than it does about how good this game is. But don't get me wrong, it's alright. The Clank gameplay is new and fun. A lot of the new stuff is fun, but it's just not as good as the original.
The movie is okay too. Definitely one of the best video game movies there is, maybe only behind Mortal Kombat. But video game movies are shit, so it's still only okay.