"Could I Have This Kiss Forever" is nice, but forgettable. Similarly, "Count on Me" and "Run to You" aren't bad, but they lack that special touch Whitney's best work had.
"Heartbreak Hotel" is so smooth. I wasn't crazy about it when I was younger, but I really adore it now.
"Where Do Broken Hearts Go" is a standard big ballad from Whitney, but it pales in comparison to some of her other ones...such as "Didn't We Almost Have It All", which is just a tremendous vocal performance from the Voice.
"I'm Your Baby Tonight" is Whitney's greatest uptempo cut; its criminally underrated! "All at Once" is also ridiculously underrated. I agree with most of what you wrote about it.
"When You Believe" is easily my favourite duet of all-time, and quite frankly, one of the most uplifting anthems I've ever heard! It always manages to calm me. It's deservedly high here.
I can't even imagine Janet tackling "How Will I Know".
I'm glad it went to Whitney; she did a remarkable job with it, though I do think it's slightly overrated. My mother adores it.
I actually prefer Chaka Khan's "I'm Every Woman" to Whitney's, which is probably the only case of Whitney not outdoing the original artist (for me anyway).
"Greatest Love of All" is exceptional, and definitely among Whitney's top tier ballads. I play it often around Valentine's Day.
"One Moment in Time" is similarly classic and special.