Happily, I couldn't have been more wrong in expectating Dollar Grills & Martinis to be some sort of naff Tex Mex. I joined a friend's birthday downstairs, in the cocktail bar that somehow manages to pull off being opulent (red and silver damask wallpaper, baroque chairs etc) with still being friendly and pretty cool.
The cocktails were top notch - you can pay more for something much less scrumptious in London - the bar staff efficient and skilled but also really friendly. I ordered what they recommended and loved it. Bar snacks were fine and the music still allowed us to chat. There was the odd mistake by staff but all very quickly rectified, no quibbles - they made an effort to ensure we were happy. The crowd was mostly 20 and 30-somethings, dressed to enjoy the evening and just getting on with the business of having a good night out.
I'd happily go back, especially with a group of friends for a celebration, and (like my friend did) would definitely reserve a table in advance.
The Martini Bar downstairs at $ serves a wide array of cocktails whilst upstairs the restaurant serves simple and reasonably priced good food.