One of the wealthier districts in Barcelona, you'll want to enjoy Eixample for its Gaudi connections, whether you are stopping to eat on the way to or from Parc Guell in the north or visiting the two residential masterpieces on the Passeig de Gràcia, La Pedrera and Casa Batlló. Both the nightlife and dining are going to tend more toward the expensive side (we are in Barcelona, remember), although tapas deals and cheap beer can be had if you know where to look.
Although there will be the more glamorous restaurants (Toto) and even expensive sandwiches (excellent sustainable eatery, Fastvínic) near the popular Passeig de Gràcia, you'll find that pretentious is not the foremost adjective everywhere you go in Eixample. Tapas giants like Cervecería Catalana and Ciutat Comtal Cerveseria have huge followings, while Irish pub/sports bar The George Payne and wonderful schtick of Obama (there's a statue of El Presidente himself) provide moderately priced drinks with superlative atmospheres.
With its shopping streets and innumerable cocktail lounges, Eixample does cater to the affluent traveler. Don't let that stop you from finding the few niches where an adventurous evening may flourish.
Note:Live music aficionados should stop in at City Hall on Rambla de Catalunya, a venue that is popular with everything from dance music to rock bands.