This is my secret weapon when I have guests from out of town (especially if they're from San Francisco or New York!). This is almost like a speakeasy--the main dining room has no windows and it's quite dark, and there are plenty of booths in little alcoves that lend themselves to looking mysterious while sipping legitimate cocktails.
There's another dining room that is much sunnier feeling, but suffers from very much out-of-place overhead fluorescent lights that spoil the ambience—when you make a reservation (and I would recommend doing so), make sure to ask for the "main dining room" and you will be all set.
The restaurant is tiered slightly, with booths surrounding an elevated bar area, which has stools and couches to sit down in—this is a pretty great place to swing by and get a drink in the center of the restaurant, but I usually go for dinner.
The music is loud and the whole place, from the photographs on the wall to the funky wait staff, has a great rock and roll feel. Everyone's super friendly (we had a great Christmas dinner here one time and everyone was super cool) and the crowd is very eclectic—you get Hollywood musicians, east side hipsters and west siders and it never seems pretentious.
I really enjoy this place. If you are visiting LA and want a fun local spot, swing by. Afterwards, you may want to cross the street and get a drink at the famous Formosa Cafe.