Snowman Attack is another survival shooter game, and there's really not that much to differentiate it from all the other members of that genre, so most of what I could say is pretty much covered in my review of The Endless Zombie Rampage. This particular game comes in the flavor of top-down, fixed turret, but other than that it bears pretty much all of the hallmarks of the genre.
One nice thing is that (as the name implies) you're fighting snowmen with snowballs, rather than spilling zombie blood and guts all over the place, making this game a somewhat kid-friendlier example of the genre (also cleaner; the zombie games always seem to end up with the ground coated with blood, whereas here the snowman remains blend into the ground nicely). One annoying thing is that the collision detection seems to be awfully sensitive -- there were a lot of times where I thought I scored a hit and the snowball went right on by.
The music is not very good -- it seems kind of inappropriate to the setting -- and is rather repetitive. The sound effects are pretty generic, and the art is definitely on the simplistic side. Overall, this is not a particularly impressive example of not a particularly great genre. Though the game does get points for the Calvin & Hobbes reference in the badge name, there's really not much to recommend it beyond that.