We have been "in" Galveston many times, but since it is a major cruise port, we are never there for too long, which is unfortunate. We started cruising from Galveston because it is an easy drive from Dallas, and we were sick of flying to Miami or New Orleans (or LA).
We know where most of the decent hotels are, we know where the Original Mexican Cafe is (highly recommended!), we did the dolphin boat tour and we've been on the State Ferry from the island to the Bolivar Peninsula.
The problem with cruise ports is that you generally arrive in the evening before you depart (don't go to the port the day you sail, just don't), and you sail out the next day. Then, you get back from your cruise, hop in the car (or head to the airport) and head home. That's what Galveston has been for us.
So, this year, we're sailing out of Galveston for Christmas, and we're going down a couple of days early to try to look around a bit before we sail.