McCarren is relatively straightforward and simple, which for an airport is just right. And this despite the numbers of people who flow through daily. The whole place is kept very clean. The baggage claim is more clearly laid out and marked than most other airports. The most complicated part is tracking the public transportation options -- there are several and the signs start to split unclearly in trying to direct people between the taxis on one side and the shuttles/limos on the other. (If you've got the time, I recommend the shuttles. They're about half the price of the taxis and you can arrange round trip from the outset.) Fortunately there are a large number of information people from the airport and several of the Strip hotels around to answer questions.
Now, the individual airline check-ins are another issue entirely -- they're pretty much awful across the board. But if you survive them, I've never had issues with security lines and there's a wealth of food, shopping, and, of course, gambling, to be had throughout the terminal in case you've built in too much time . . . which, in my experience, is rarely an issue. (Just to re-cap: McCarren, good; airline check-in...just grin and bear them.)