Pappadeaux is not cajun, it's just seafood.
If you want really good Cajun food go to Dodies on greenville, but you'll have to put up the the LSU flags and memorabilia, best Cajun food I've had outside of N.O.
A second, third, and tenth vote for Bobs. It is incredible, don't let the look of the bldg. fool you. Get your reservations early.
Desperados is good, this native San Antonio person would recommend Ojedas, Herrerras, or Avilas on Maple before Desperados. Blue Goose is terrible, might as well just get some frozen El Patio from the store and nuke it (my opinion, I know its a popular place).
There really is NOT a lot of great BBQ in Dallas - Sonny Bryans and Dickeys are local chains that are good enough. Bakers Ribs is popular, the only place you are going to get primarily pork BBQ is Red-Hot-& Blueon 75 and Walnut Hill. There is a very good BBQ joint downtown behind the Fed building calles Sammys, there is also one in Preston Center (NW Hwy and Preston Road).
For nightlife I recommend west end (touristy but good for out of towners, very few locals go there), Uptown (near downtown, good 30-40 professional mix, go to The Gingerman or TABC), Deep Ellum (good for students and 20-30s, ecelctic mix of bars & restaurants, best honky-tonk country bar in Dallas is there - Adairs), or Greenville Avenue, which extends from Ross all the way up to Mockingbird, anyone would be comfortable here. If you are looking for a really posh place to drink that is not crowded or insane, hit The Library Bar in the Melrose hotel. There is a Gilleys (of Urban Cowboy fame) near downton across I30 that is Dallas' answer to Billy Bobs Texas in Fort Worth, a good Texas singer-songwriter is playing New Year Eve - Jack Ingram, if you like the Driveby Truckers or Robert Earl Keen or Cross Canadian Ragweed or Chris Knight, you would probaby enjoy this for NY Eve.