It is good? Absolutely! We use it at work for MIDI-based Hip Hop projects all the time, and I score video projects with it. No one complains at all about the MIDI functionality.
It is, however, among the least full-featured MIDI packages out of all the major multitracking programs. Word on the street is that Sonar and Cubase SX, and Logic on the Mac-only side of things, all have better MIDI features.
I guess I just don't need fancy MIDI features so I don't know what I'm missing, but the sequencer in PT does the job.
Take care,
Chris