Many people love SW. I usually fly them when I go to Vegas, or if their prices are substantially cheaper than Delta. Southwest has a good record on safety and equipment maintenance. My only real 'gripe' about this airline is that they don't have assigned seating. Check in early for your flight, especially if traveling with a group that wants to sit together. You will be given a numbered boarding pass at the gate area. They will call for boarding in order of these passes (like 1 to 20, 20 to 40 etc.) Special needs boarding (wheelchairs, non-accompanied children) pre-board as with other carriers.
There are a few seats that face backwards. I've sat in them once, they weren't bad, but avoid them if you are prone to motion/air sickness as the sensation is the opposite of what your mind/body expects.
When your boarding pass number is called, you can enter the aircraft and pick any seat you wish, the cabin is all coach. Their will be no meal, but they usually have trail mix or similar munchie along with beverages. On time performance is above average. They've added some newer model planes lately, but most of their fleet is 737s, 3 seats/aisle/3 seats.
Again, by all means, fly them if the price is right.