Its been a while since I have flown with Jet2 but have just returned from a week in Rome flying from Manchester and found them spot on. Fast easy check in, comfortable aircraft (737, 24 years old but so what) and departures/arrivals on time or early. In flight food was good as well.
It occurs to me that if Jet2 want to expand at Manchester, maybe they should try long haul. 3 times weekly to Cancun for example would be popular as the only current option is TUI, whos service on that route was woeful last year.