I was pleasantly surprised with my trip from Charlotte to Las Vegas on Spirit Airlines. Based on all of the reviews I'd read, I had really low expectations. Yes, they nickel and dime you for everything but they are very up front about that. I found that if you plan accordingly, the flight is as good as, if not better, than the major airlines.
We bought 1 checked bag each and an earlier boarding zone as part of our tickets so we didn't have to worry about any extra charges on the day of our flight. Every employee we interacted with was pleasant and helpful, more so than I found the employees of American and Delta the last times I flew. The seats and leg room seems comparable to other major airlines. The seats don't recline but that doesn't bother me and I actually prefer not having the person sitting in front of me being able to recline. They don't have any charging ports for your electronics so you need to bring a backup battery if you want to charge during the flight. And they don't have full size trays so if you bring food on you need to eat it on your lap. I did find it impossible to sleep on our redeye flight home but that is because we didn't come prepared with neck pillows or eye masks.
Our checked bags came out quickly once we got to the baggage claims in each city (again, better than I've experienced with American or Delta recently). We had a connection through Orlando on our way to Vegas, which made me worry about luggage being lost but both bags made it safely.
I would definitely fly Spirit again for a domestic vacation.