A lot of people on the forum complain about airlines because of their lack of service items onboard an aircraft, so I would say you are going to get a lot of complaints about Spirit.
While I haven't flown them, I have heard that they are a decent airline. No frills, so don't expect a meal, but they are cheap, which in air travel today is good.
Recently they have had some maintenance problems that worry me, but that seems to have changed for the better. Like any airline, they have their good days and bad.
If you aren't going to freak out because you aren't served filet of pigeon on your flight, or the fact that you may fly on an older plane, then I think you will be fine.