Atomic play the same sort of stuff as Pean, Slumberyard and the SurfGods, but not as well. It's impossible not to compare them, and the others are much better, although Atomic did a good job of some songs. The singer's voice does not seem to suit most of the songs (more suited to musicals), and the band as a whole messed up a few times - maybe they were nervous.
Admittedly the crowd was small, but Atomic still did not seem to have a very good stage presence. I've been to gigs where there were about 20 people in the place, but with seemingly little effort the band on stage got the crowd involved. Atomic didn't manage it. Many bands that are not top quality overcome the fact that their music is not of a super high standard by their stage presence. Unfortunately for Atomic they didn't pull it off.
They did however do some good Chilli Pepper songs, and some of the Blink182 and Pearl Jam songs did not sound too bad.