I was either at the top of my game or got lucky when I played this, because none of the bosses took more than three tries (on normal), but I could tell they absolutely should have. I agree completely about certain bosses feeling cheap and unfun, and at times the traversal sections just felt like a chore. This game certainly has some decent ideas, and when it's not trying too hard, some of the humor/craziness is great (loved all the pickup weapons, Yaiba's single track mind, and the final boss).
Overall, I think Lolipop Chainsaw does "weird ass zombie killing game" better, and Revengeance does "action game that doesn't give a shit" infinitely better, but this was definitely worth playing.