The story doesn't really deliver the same level of manic charm or clever humor of the rest of the Ratchet series, but the game does (more or less) faithfully replicate the familiar platform-hopping, gun-crazy Ratchet formula. The controls feel stiffer than usual, thanks mainly to awkward strafing and a slow-to-turn camera that frequently gets stuck on objects or spazzes out for no reason, but underneath that gauzy layer of clunkiness, Size Matters still feels like vintage Ratchet, with fun level design and a nice balance of gunplay, gadget-themed puzzles and bottomless pits to fall into.
Ratchet himself also packs a pretty impressive arsenal by game's end, consisting of eight gadgets and 13 weapons, which upgrade automatically as you use them and can be further augmented with between one and three black-market add-ons. In general, the guns are pretty similar to what's popped up in previous games, although some of them - like the default Lacerator blaster and the Suck Cannon, which inhales small enemies for use as ammo - are practically useless in the game's ridiculously tough final stages, where it takes like two rocket-launcher blasts just to take down a small guard. And that's to say nothing of how weak your weapons are against the later bosses, who can kill you in just a few hits after soaking up all of your high-powered ammo.
That said, Size Matters does introduce a few interesting new elements to the mix, chief among them the way the game doles out armor for Ratchet by scattering it around in pieces (helmets, gauntlets, boots and body armor) for you to find or earn through minigames. Complete a suit of matched armor, and you'll earn a power-up - like a flame charge for Ratchet's axe-like wrench - that'll last as long as you're wearing the full set.
There's also the shrink ray suggested by the title, which enables Ratchet to pick locks by hopping into them and completing a grind-rail sequence. But because you can't shrink whenever you want - like, say, to get tiny and then explore new areas within levels you thought you'd cleared - this is little more than a gimmick with almost no effect on the actual gameplay.