I just got through beating this game, and had sort of the same problem. Eventually I think I accidentally broke the bridge with an attack and it let me progress, but prior to that point I was just stuck fighting endless waves of guys wondering how to progress. So, I think there's a way to chop up the "bridge" (the game treats it as an obstacle I think) to proceed. Either that or the game just makes you fight for a ridiculous length of time before it lets you move on. Rage-inducing game IMO.

Okay, it's been over a month, but I had initially decided that I had enough of this game after not getting past this part. After getting a new computer, installing the game and starting from the beginning I got through the level without any problems at all. The raft ride was totally smooth this time and I only got stuck at those rope barriers where you're supposed to get stuck, so I dunno.