A fun game, but a little short and devoid of serious challenge.
The graphics are pretty good. Everything is big and detailed, and although the environments aren't big on textures, they are big on charm. The space flight sequences are really nice, and I like the Colony Wars-like flowing space and the lighting effects.
Sounds are forgettable for the most part, I don't remember any of the music tracks enough to say they are exceptional in any way. However, none of the music is annoying either. It gets the job done.
Gameplay: You're a furry creature with big ears and even bigger guns with a little robot sidekick. You use your trusty wrench and guns to beat and blast the bad guys. You can jump, double-jump, high-jump, hover and long jump in addition to using the various weapons (some of which are kind of nutty, like the Bee Mine Glove) to overcome obstacles. There is a lot of variety to the gameplay, including "skyboard" races, space dogfights with a giant Clank and various minigames also featuring Clank, which reward bolts (the game's currency) and armor fragments. Some of the weapons are great (the Shock Rocket and Agents of Doom/Dread are my personal favorites, and you gotta love the Dual Lacerators) and others are fairly useless (the Suck Cannon is aptly named for more than one reason). It's neat that every weapon can be upgraded as they're used, growing more powerful, and that you can buy "mods" to change the attributes of the weapons as well.
I felt as if, most of the time, the camera was zoomed in way too much on Ratchet, making it difficult to navigate some of the environments or keep track of all the enemies attacking you. This was especially prevalent on the trippy Dreamtime stage, where the view is framed by fuzzy cloud-like effects, giving the effect of being in a crazy dreamworld. It worked, but it was also a little hard on the eyes and made some of its areas unnecessarily difficult to navigate.
The play control is spot on, though I would have greatly preferred to have L and R as the strafe buttons instead of the D-pad. That little error in judgment on the developers' part (at least give me the option to change it) made me almost never use the strafe function. It was just easier to move with the analog nub, rotate the camera and keep focused on my target.
I say the game is devoid of challenge because, besides the loss of a few moments' progress, the player isn't penalized in any way for dying. In fact, it's almost beneficial because you always keep the experience points, weapon experience and bolts you get, so the more you die and come back to the same area, the more powerful you eventually become. The last boss was pretty hard, being capable of killing you in two hits even at maximum experience level (protip: use the static shield), but once I learned his pattern and made use of the right weapons, it turned out to be a cakewalk.
However, there is some challenge to be found in some of the more advanced levels of the minigames. I almost threw my PSP in frustration after getting repeatedly destroyed in the Clank arena challenge called "Tom Saw-Yer" where a bunch of sadistic robot farmers and lambs bum-rush you without mercy with pitchforks and running tackles, your only defense being a spinning saw attack that did next to no damage to the opponents and took time to recharge after every use, not to mention being surrounded by burning and freezing traps.
The game has a few online multiplayer modes, but they're only remotely fun if you've been doing it for a long time. I haven't. There's just too much dishonesty and dishonor out there for me to play competitive online games. Too many quitters, too many people making secret alliances, too much crap. However, if you're into that sort of thing, it's there for you.
As far as replay value, a challenge mode is unlocked when you beat the game. In that, you run through the story mode again, you can not only get more life than the normal game's maximum of 50, you can buy new (and really expensive) versions of your weapons and fight tougher enemies. You also start from the beginning with every piece of equipment you ended the game with. I'll probably run through it until I get bored. There are also several armor sets to find and earn via the minigames, and when you complete a set, you get a special ability. The Electroshock armor was enough to get me through the game, and the minigames are either too frustrating or too tedious for me to run through.
Overall, I'd guess Size Matters is not much different from past R&C games, so if you enjoy the series and have a PSP, go get it. But for me, it was fun while it lasted, but too short, too easy and the bonuses too much work to acquire. Not a bad game though.