Jay's not wrong, but there is some stuff. The Old Port is the area drinking spot Maine's attempt at nightlife. There is a small civic center where you can see the Portland Pirates play hockey (when does the season end?) and some bands too (I think
Motley Crue played/is playing there on this tour). There's also Hadlock Field where the Portland Sea Dogs (Red Sox AA/AAA team) play. As far as guitar stores. There's Daddy's Junky Music (mostly low end and secondhand stuff -- the local one to me does have a BRMR Jem, however) and Buckdancer's Music. They carry Mesa/Boogie, but I've never been. There might also be some mom & pop stores I'm not aware of.
There's some nice scenery/waterfront, restaurants, a big mall (South Portland) etc. but it's not someplace you're likely to see on that E! show that highlights party spots.