Frequent business luncher in that area of the Loop. Generally bleak, but the best bets within a minimal walk, by far, are Rittergut (wine bar in the "old" Merc adjacent to Rivers) and The Florentine in the JW Marriott. South Branch has a Manhattanish or maybe Miami-like after work scene in warmer weather with the outside bar, but the restaurant is basically no better or worse than the formulaic Loop Office Building Lunch and Happy Hour Drones brought to you by the insidious Restaurants America group. These places make a good enough first impression with their furnishings and they clearly know what developers and landlords want in the lobby of A+ office space. But a few meals will reveal them as, at best, slingers of fried calamari and sliders by the numbers. South Branch is not part of the Restaurants America clone army and is a minor step above them. But the other places I mentioned above actually have pretty good food and interesting drink. Florentine, part of the BLT group in a classy hotel isn't surprising. Rittergut, a local-ish wine bar from the Rivers (a tired spot) people with an oddly Tyrolean theme is.
In my efforts to dissuade coworkers from ever meeting at any of the generic Loop lobby slider spots, I did some looking around. Try to figure out what's what in the various restaurants below, many within a block or 2 of each other in the Loop. Notably, the non-Chicago outposts of this empire tend to be lobby fillers in those weird new mixed-use phony "downtowns" dotting the Sun Belt exurbs 20 minute tollway drives from Dallas, Scottsdale, Tampa, Ft. Lauderdale, etc. Perfect.
http://www.restaurants-america.com/PS, I should mention that the lamb burger and the Nicoise salad at Rittergut are both really very good; the former was a juicy, gamey, rare, revelation the latter was simply correct in all ways, which I can't say I'd otherwise ever had in Chicago. Florentine has been well enough covered here but I'll add that their happy hour is batshit crazy and probably can't last too long. Free wood fired pizza, made to order, whatever kind you want off the menu, plus daily beer specials. I think I ordered a $4 beer (Bell's Two-Hearted at the time) and ate 30 buck's worth of fancy pizza the last time I visited.