They just started flying out of Long Island this past fall. My experiences to date ...
October to Orlando - our daughter had emergency surgery 48 hours before we were supposed to leave - Frontier has a great policy in place for illness, including family members. Based on the instructions on their website, I provided a note from her doctor saying that I needed to stay home and take care of her. I contacted Frontier through an email form and included a copy of the letter. 2 hours later I had credit for my flights that would be good for 6 months. I used the credit to get tickets for a November trip, and the flights were cheaper and there was still some money left on the credit that I used to pay for a checked bag on a flight in December. (Disney was also fantastic and credited me back my room deposit even though I cancelled after the 5-day limit).
November to Orlando - on time outgoing, 30 minute delay return trip.
December to Orlando - on time both ways.
January to Fort Myers - on time both ways.
February to Orlando - on time both ways.
We have paid for one checked bag between the two of us ($30 each way, pricing differs based on time of year and route). But, we have also done personal item only and have easily gotten 4-5 days of outfits in. On multiple flights we have been able to put our personal items in the overhead - we had one flight where the attendant stopped everyone from doing it.
The seats are not the most comfortable. But, personally I find them more comfortable than the seats on Southwest's new planes. The little tray table is annoying. I find the leg room to be about the same as SW.
We usually pay for a seat ahead of time because we both like aisle seats.
I don't care about having to pay for food since I always bring a bottle of soda or water on the plane since I prefer not to have a cup of liquid that can spill on my tray table when I'm flying.
I can put up with all the little inconveniences for the price and the short flights (it's about 2 1/2 hours). I would have to think hard about a flight longer than 3 hours since we have so many other options available to us in the NY airfare market.
I will say that when we were flying to Orlando in February, there was an absolute nightmare going on about a flight to Tampa - it was scheduled to leave around 3:00 pm and they kept delaying it 30 to 60 minutes at a time, they were still waiting when we took off on time at 7:00 pm and it was supposed to leave at 9:00 pm at that point. I checked the flight status later and it did not take off until 11:30 pm. The Frontier staff communication was horrible.
Would I fly them to get to a cruise or a special event? Probably not
One more thing - people buy way more alcohol on Frontier flights than I ever saw on our Southwest flights!!