I've been at the San Francisco Giants' ballpark before a game, and had to stand up and listen to some lounge singer lay his stylings on the National Anthem with a trowel, and by the end of minute 2, I was looking askance at the heavens.
The trick with melisma in an R&B song is to use it with restraint. Using melisma for a particular phrase in an otherwise understated performance calls attention to that phrase, and communicates angst or joy at a deeper level than the more matter-of-fact actual lyric. A perfect example is Sam Cooke's "Lost and Looking," which is just his voice and a stand-up bass. It's an incredible performance: