This game is very well done! I'd highly recommend it to anyone who's a fan of 3D platformers!
Unlike the typical games of its style, A Hat in Time only has one major type of collectible, which are Time Pieces (pretty much the equivalent to jiggies). The other collectibles (yarn and coins) are useful because they allow you to make new hats and to get rewards like new songs and new colors for Hat Kid's clothes, but you don't really need collect every one of them, which is kind of relaxing compared to usual collect-a-thon type games.
One thing A Hat in Time does better then most games out there is that it gives sense of exploration, adventure and wonder. It makes you feel like a little kid playing on giant jungle gyms, which is feeling that no one has really managed capture better than this. There aren't a lot of levels, but they are all pretty expansive and have all sorts of interesting things laying around. Personally, since I LOVE the picture mode (you unlock it pretty quickly in the first level), I spend a lot of time just goofing around in each level to find fun new spots to observe and capture on film.
I'd also like to note that while most bits of the game are pretty easy, the charm and story surrounding each mission makes it easy to forget that there isn't a lot of variety in the combat. Quite frankly, combat feels like it isn't the point, and for the most part, that isn't a bad thing.
Like many have mentioned, this game is relatively short at the moment (unless you spent a lot of time screwing around with the camera mode) and has some minor glitches in certain parts (I still can't figure out how to fix the camera mode filters

), so be aware of that. This game probably also won't appeal to anyone looking for more serious and challenging tasks since quirky humor and expansive exploration seems to be the clear emphasis. Just be aware of that in case you're looking to check this game out.
I'd strongly recommend checking out this game. It is definitely worth the while.