I had my 25th birthday party here a couple months ago, and had a great time. I had actually commissioned my boyfriend with the task of making bottle service reservations in the city, but he waited too long and a week before the celebration, I still didn't have a venue settled. We ended up contacting Village Underground since I knew some friends who had had parties there before, and while there was some initial confusion re: bottle service list vs. guest list, we squared things away with Gypsee, the FBPC event planner, and things went off without a hitch. Gypsee seated my party as soon as we got there, our waitress took good care of us the entire evening, all of my friends got in without any issues, and the music was great for dancing (hip-hop/pop) the whole night. Predictably, bottle service was pricey, especially with the mandatory 20% gratuity, but that's par for the course in Manhattan. All in all, if you're willing to do bottle service and have "good dancing atmosphere" as a prereq for a party, I'd definitely recommend Village Underground.
Pros: great music, great dancing atmosphere, no-drama bottle service reservations
Cons: can get extremely crowded and cramped on the dance floor