Frontier elite member here. Actually doing a mileage run tomorrow to Orlando for the day to keep my status for next year. Landing in the morning, driving to Disney to spend the time before my return flight in the evening. The flight was $28 RT.
I have been flying Frontier about once per month for the past 2 years. Personally, my husband and I enjoy the airline. It is what you make of it. And once you make elite status, it becomes even more pleasant with a free carry-on and free seat selection (other than extra room, but if one of those seats is open at check-in time you can change to that seat for free - as I did this morning).
We have a lot more flexibility than many people.
I find the seats to be not really be any less comfortable than Southwest or Jet Blue. I have not tested this theory on a long-haul flight though - most of my flights are in the 3-hour range.
I have been able to pack for a week-long trip to Disney in my personal item multiple times.
I always bring my own snack and soda on the flight - always do regardless of what airline I fly. I prefer to have a beverage with a cap, instead of worrying about a plastic cup on my tray.
My flight times have only changed a couple of times and by less than 30 minutes - this occurs when they announce new routes and eliminate others and start juggling all the planes along with it. They re-arrange routes a few times per year.
Most of my flights have been relatively on-time.
These are the 'incidents' we have encountered in 30 legs in a little more than 2 years ...
I have had one flight returning from PBI cancelled while at the airport because of weather. I was rescheduled 2 days later out of Orlando - this can definitely be a hassle for a lot of people. But, I had someplace to stay in in the intervening days.
I have had one flight diverted to Philadelphia on our approach to our home airport - the fog was too low. By the time we landed in Philadelphia, most of the NY area airports had been shut for incoming flights because of it. We had to stay overnight in the airport (5 hours), were given a meal voucher for breakfast. They made a new flight for 6:00 am to bring us all back to NY.
I had one flight delayed by 2 hours leaving out of MCO - given a meal voucher and had a $75 credit in my email when we landed.
In October we had our first major incident with a mechanical problem - we sat on the tarmac for a couple of hours. They went back to the gate and everyone got off the plane and were told to wait in the area while they tried to fix the problem or you could change your flight. Chaos ensued at the gate, but people were generally calm. Many changed their flight, electing to leave out of other Florida airports in the coming days. We were pretty sure, based on our experience, that they were going to get that flight out. If it wasn't that night, it would be a newly added flight early in the morning because they needed that plane back in NY for the next day's schedule. We were correct - we left 90 minutes later. We were each issued $200 vouchers. The original flight was $24.
I have had to change flights a couple of times because of travel advisories both because of hurricanes and snow - easy process and it was announced a reasonable time before the flights.
I have elected not to change flights in the event of a travel advisory and we flew as originally scheduled.
I have had planes leave in the lead-up to snow events, while Southwest out of the same airport was cancelling their flights days before the snow event even started. It turned out the weather was a non-issue on flight day.
I have had long delays on Southwest and Jet Blue flights in the past couple of years. Along with flights on SW that were on-time.
If anyone has any specific questions - I'd be happy to try and answer them (i.e. way seats are assigned on check-in if you did not pay for a seat, better places to sit when trying to spend the least amount on a seat, boarding process, etc)