I must give a plug for the new Lobby Bar + Kitchen in the Greenway area of Boston (on the edge of the Financial District, near 93 and the waterfront). Sadly, the restaurant doesn't have much of an online presence yet (beyond this stuff@night blurb and this Yelp mention), but it's official opening was just 2 weeks ago so hopefully more content will come in time.
It's a very small place, but perfect for the 10-person birthday dinner I shared there last Friday night. It has a dark, modern interior that feels more NYC than downtown Boston, and in just one small room a smattering of dining tables, bar stools, and comfy lounge chairs.
The menu was pricier than I'd anticipated ($~30 entrees) but well worth it: I enjoyed baby lamb chops with mashed purple potatoes and baby carrots, while my companions enjoyed filet mignon, short ribs, and pretzel-encrusted tuna (delicious), among other things. Everything was well-prepared and served by very friendly and attentive wait staff (although the main dishes were a bit slow coming out, perhaps because we had such a large party).
Lobby Bar + Kitchen is a great new addition to downtown Boston, probably best suited to smaller groups, but would make a nice Valentine's spot :)