My wife is the bigger Whitney Houston fan in our house, but I'm a fan, too, one of those supposedly guilty pleasures that I never felt all that guilty about. It was the voice, and the formidable technique behind it. She was a real diva, in that she could make a mediocre song into something great, and a great song into something transcendent, through sheer vocal splendor. This is still far and away my favorite:
"How Will I Know" is a perfect symbiosis of song, production, and voice. It's a great exception to the rule, a pop song that modulates down, rather than up, at the climax. This is solely to take advantage of Whitney's high belt voice. (That you could talk about her voice in strict classical/music-theatre technique terms—chest, belt, high belt, head voice—indicates how much more solid and finely-honed her voice and technique were than anybody I can really think of in top 40 today.) Her belt topped out around E-flat—impressively high—and for the first two-thirds of "How Will I Know," she's deploying that E-flat in every chorus. Then the song modulates from G-flat-major to E-flat-major, and that same E-flat now sounds a third higher, an upper octave rather than a sixth. It's at once brilliant sleight-of-hand arranging, a singer who knows exactly what her voice can (and should) do, and a sign of where the song's real power center is. She could have extended up past that E-flat into head voice—she does so elsewhere in the song—but the thrill of the high belt is what the song needs, so the whole thing reorients around that one note. Timbre trumps harmony, as well—in this case—it should.
I keep thinking that the race she lost is a race that all singers run, and all singers lose; even the most powerful voice can't defeat time and decay. Whitney ran the race too hard and too fast, but at her best, in those years when she really was incomparable, her singing had a quality that so many great singers have, that of euphoric resistance. There are singers who acknowledge mortality, and break your heart; but Whitney was the other kind, shouting away death, even just for a while, with defiant joy.