I just played horde.... WOW

[Infamous]

Try playing it on insane, you get 1-shotted by Bloodmounts (and almost everything else..) ;_;

Here's a tip: Play with friends until you learn each map carefully. There are spots in almost every map you'll need to hole yourself in to survive later waves.

The easiest map to get to wave 50 in one shot would be Security, just hide behind the lasers and when there's one locust left then everyone goes out to get ammo. Place boomshields around the lasers for extra protection (in the later waves/higher difficulty they will press the button on the opposite side to lower the lasers and flank the fuck out of you).