A note on neraine's stragies. If you combine the dodge build, with leviathon and the 2x deep blue equip, it works really well. Dodging attacks with leviathon puts all enemies in a chrono lock, and deep blue freezes them normally, so anything that gets through your offense and hits you, causes a freeze which lets you clear the screen. You still get a good freeze bonus against the bosses too so it makes for a potent combination.
Wave 173 second try. It's the bosses that get you like I said, because if you don't target them, they get through, but if you do, then all the normal guys get much farther without being damaged, then you can't stop them in time either... I'll have to try to get farther.
Pardon me if this has already been addressed, but you should make the specials different for each race. Instead of them all having a meteor shower, maybe just give that to the orcs because they are fire, and maybe a thunder storm for the humans, and blizzard for the elves.
I don't know if it's been posted or not, but it is possible to get a rank of grandmaster in this game, not just master. Flipping off of a wall and then immediately killing a person along with not being spotted and having all stealth kills will get you grand master for a level.