He is typecast as that cynical, satirical, crude, womanizer, alcoholic... it's what he does best and he'd pretty damn good at it. And I think to a point, his fans expect to see that. That being said..
However, Rescue Me is a really great and at times biting drama that I think is Leary's best body of work. Where it can be humorous at times, you will see a dramatic side to him that you probably haven't seen before. If you haven't seen it and you even remotely like Leary, you should make a point to see it.
Rescue Me/Leary has been nominated for the Satellite Award for Outstanding Actor, Golden Globe for Best Performance by an Actor in a TV Drama and an Emmy for Outstanding Writing for a TV Drama. Sadly not winning any but still the recognition of being nominated in both seasons of it's existence.
Speaking of Leary, he will be on Jon Stewart's The Daily Show this coming week if you want to catch one of his appearances.