I flew them last year and they were fine. Not great, not terrible, but fine.

One nice thing is they offer fairly cheap paid upgrades to business class through a program called OptionTown -- if you have a longer flight it's worth looking into. I paid something like $100 to upgrade on a JFK-MEX which was well worth it IMO. Not sure if it would be available if you are booked on a Delta codeshare though.