I've finished campaign on Insane solo and finished horde on casual with a mate

. The match making system is quite poor and the story is a bit weak - "It's a giant worm, they're sinking cities with a GIANT WORM!", I mean seriously.
If anyone is having issues with horde; go on the map "river", get to wave 8ish and kill a mauler, pick up it's shield, go into a house and plant it on the stair case. It stops any enemies from getting passed, after that you can pick them off from a distance.