Effin' Great!
A totally addicting game! I've got done all the achievements except for the one where you need to eat 5 brains. I've beaten the game like 10 times with various characters and there hasn't been enough brains. :(
But anyway, if you're having trouble and you don't have as much patience as I do to figure out the boss strategies and meanwhile you're yanking out your pubes in frustration like I was, here ya go, my personal strategies to beat the bosses:
Boss 1: If you're using a fast character, try to time running back and forth so that you can get the boss to hit himself/his minions with his launch attack. Otherwise just pummeling him will be better.
Boss 2: Bombs away! He doesn't move very fast so bombs work well on him.
Boss 3: Don't make it a priority to make the boss use his rockets on himself. Try to use bombs when he's about to get into a horizontal line with you. Run around a lot.
Boss 4: Try to ignore the hatless dude when he transforms and focus on the hat wearing guy. The hatless dude will counter your attacks ONLY IF you are in range of them. Your character has a longer range so as long as you keep him at weapon's length away you shouldn't get hit once from him (this is after you take out the hat guy).
Boss 5: It took me too many tries to beat him, but I've figured out it's best to try and separate the zombies from the main boss. If you're all clustered together, what's going to happen is a zombie will bite you leaving your vulnerable for the boss to launch his shoop da woop, crippling your health.
Overall strategy: When you solve the combination for the chest, it's the same throughout all playthroughs, don't grab any innards until you reach it. One thing to always remember is to not let yourself get flanked by enemies! And when you're getting the Horde Fighter achievement remember that the zombies have a shorter reach than you, so just as long as you don't get too close and keep them far from the boss you'll be fine. I hope this helps you beat the game with your pubes intact!