I know about all the extra weapons, animals, and fighters, but I'd really like to know how long the main game is before any replays.

5 hours.  If you're good.

"5 hours.  If you're good."

Well, there are a couple modes I didn't try, and I didn't bother doing the arenas.  But yeah, after playing a little single player I went online and me and one other guy ran through the whole thing in about 5 hours.  I think we got kinda lucky though, when playing again later today with a group of 3 people we kept getting killed over and over so something like that could add a lot more time. 

Even after beating the game, you can continue with the same levelled character on harder difficulties to keep getting more skill points and better weapons.  I can see myself playing this game for a long time, it's very charming.  

"SolemnOaf said:

"5 hours.  If you're good."

Seriously? I thought it would be at least an 8 or so hour game."

I've sunk quite some time in it, and there's still plenty of game left. I love it! Fart jokes ftw!

I think I went though in 6 hours, 5 probably.  Total hours are around 27 hours, and counting of course.  Replay value is huge on this boys, gotta unlock em all!  I still haven't completed insane tho the second boss is seriously tough.

well i played through one of the early levels twice and unlocked three extra weapons in the second go. There is a lot of replayability here for the completist.

I can see myself replaying alot here in co-op, building up unlockable characters.

I bought it on Wednesday and just finished now.
You're gonna get really short answers from here, because most internet nerds play games like non-stop crazy. So it's a good rule of thumb to take most answers you hear in forums and  times it by about 3.