I have a love-annoy relationship with them. I've organized it into a list for your reading pleasure:
LOVE: the schedule of frequent flights to places I go, ease of buying one way tickets, free bag check, easy online check in, decent mobile phone ap, no change fees, easy to deal with when you miss flights or plans change, GREAT free flight system.
ANNONY: they keep restricting the drink tickets and they're not consistent about what they can be used for, cheap flights attract some annoying seat mates, for some routes they only have flights with stops and competitors have direct flights, no tequila served on board.
Overall, I fly them on flights under 3 hours. But no airline is perfect.