Some of the best restaurants in town are downtown, but most of it is either fairly pricey or loud (depending on what you consider pricey or loud), or italian.
The West End district (which is within downtown) has some chain-type restaurants like Landry’s which serves respectable Cajun seafood.
There is a decent restaurant at the Westin City Center, quiet and reasonably priced. Probably won't write home about it. There are some downscale Mexican joints downtown, but tend to get loud depending on the day and time.
If I were dining alone downtown I might eat at the ceviche bar at Stephan Pyles, have a glass of wine, a salad and a tapa or two or some ceviche. Probably under $40 or so. It'd be a lighter meal but guaranteed to be good. It’s an upscale place but the ceviche bar is meant to be less formal.
Dallas Fish Market at the corner of Main and Akard is excellent. White table cloth moderate price, good wine selection. I'll be eating there Friday.
Less expensive just to the east of the Dallas Fish Market on Main is Sol Irlandes (means Irish Sun in Spanish) good Mexican Food.