I played it about five hours on Saturday, most the day Sunday, and a couple of hours Monday and Tuesday... (Played it some today, but that was after I finished it.
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It sounds like you rushed through the game. What did you do, hold down the run button the whole time or something?
LOL, I can't even hope to hold the run button down when playing with others because people get in my way and end up killing me 
My copy came in the mail today. Very excited to play some more.
If you can, hop to the front of the line, the front of the screen, and outpace the people giving you trouble.
If not, you'll just have to space yourself so you have room. What I've found when I play with my roommate, is that if I go first, he insists on running right behind me, providing no room for error or a reduction of pace to be careful. Since that's the case, I often let him go first, so I have space to play how I like.
Of course, he's a bit wishy-washy, because when I'm not in front, he'll either go very slowly or, in places where one player goes through the path, and the other waits for traps to open and allow another player through, he'll run as fast as possible, to cause trouble for the player behind.
In essence, I'm saying he figures out the most annoying way to play based on what I do, and does exactly that. It's interesting, and is an element of the game, so I can't truly complain
