Natt Spil... it's alright. I'm between 2 stars on it's lousy and over crowded nights, and an easy 3+ stars on the nights when it's the right size crowd, the windows are open, and I'm getting food. So... let's break it down...
Cash only. 'Apps' is the food here, for a snack. Beers/drinks aren't anything special, with a moderate selection. If it's incredibly packed, don't bother with food... you'll just feel in the way. They do serve late (not sure how late), so that's nice if it's a weekday. Go with someone who has been there before if you can to avoid what other people mention about it being 'confusing'. The crowd is generally very casual.
The best thing is that if you're downtown, you can 'try it out'... because if it sucks for you that night, walk somewhere else. I'd definitely say to give it a go.