if you could squeeze all the bad things about las vegas (crowds, drunks, grime, traffic) into one huge building, you'd pretty much be looking at McCarran. As much as I love Vegas, I would rather dive head first into a swimming pool of thumb tacks than spend a five hour layover here.
ps: good luck if you are on Southwest and have to transfer from B15 to C10. I almost stole and wheelchair. that first (and only) short as hell moving sidewalk is like a huge slap in the face.