Any Really Good Don't Miss New Restaurants in Bangkok?
For upscale (and ultra upscale), I heard good words from Nahm (The Metropolitan hotel, Sathon area). Also, Sala Rimm Naam (Mandarin Oriental, Charean Nakorn area) and Spice Market (Four Seasons, Ratcharamri) are nice. Sala Rimm Naam usually have Thai performance during dinner (but I'm not sure coz I don't go for that).
For mid-range, Curt always recommends Rossabieng (which I heard good words from Thai friends and have always wanted to try but it's quite far from my place). Nara at Erawan Shopping Center basement is also a good choice. Som-tam-nua at Siam Sq is one of my favorite (this won't be generic central Thai food rather it serves north-eastern Thai food aka I-saan food)
Rosabieng has two locations, one at Sukhumvit soi 11 and the other across from the Samsen RR station. If you live in the northern suburbs, Samsen is better located.
I'm not a "new tables" kinda guy. I prefer old tables, like Krua Apsorn. If I had only one place to recommend, it would be Krua Apsorn, and their curried crab, crab omelet, stir fried morning glory and/or ดอกขจร.