He's very good at marketing his airline (often with outrage inspiring press releases) and very good at finding ways to squeeze more blood out of the stone of budget travellers. I don't really care whether he's "good" or "bad" but I would like to see the regulators shut down more of these aggressive tactics as they emerge.
Bezos invented 'your margin is my opportunity' (at least that's where I heard it first), but O'Leary has that phrase in his blood instead of hemoglobin.
I just wish the airlines were forced to put their booking behind an API so we could book flights without having to go through mazes that are different for every airline.