I was really excited about Southwest from all the thing people here were saying about them. But I have to say, they seem a big lacking for regular travel:

1) I usually try to book the cheapest flight (with the exception of UA, who I wouldn't fly if it was free). Most of my travel, for business or leisure, takes me between major cities, like SFO and NYC, LA, DC, Chicago, Dallas, London, etc. I have never found WN to be the cheapest flight on these routes, ever. I'm sure it happens, but legacies seem to be pretty competitive on these routes. I usually end up flying AA, because they undercut WN. I can get a cheaper fare on AA and upgrade to first, which, even if I have to pay for sticker upgrades, still comes out cheaper than flying in steerage on WN. If I flew a lot of very short haul flights, I could see how I might prefer southwest on price and directness, but most of my travel takes me between cities with large populations that are well served by the legacy routes. I would suspect that most of the big Southwest fans are ones that frequently fly direct short-haul flights between cities that happened to be served by Southwest. Also, when you're flying a 6-11 hour flight, business and first class make a much bigger difference than if you just on a plane for an hour or so.

2) The boarding system (even the new one) is innane. Letting people pick their seats on board inevitably leads to people sitting up front first, then moving backwards, for the most part. So you have to wait for everyone to put their carryons away and sit, and then you move back a little find open seats, and repeat. While the crew is remarkably efficient about getting planes out quickly, the boarding process means you're constantly waiting. in contrast, most legacies board from the rear of the plane forward (with some exceptions), which means that there is less waiting. IME, Southwest has the worst seating system of any carrier.