For you, Georgi, I would recommend either 12 Play or Love Letter (the latter being my favorite, good call Dreamcoil).
12 Play is probably his most classic album. It really shows his influence on modern R&B, and you can tell that this album specifically was a huge influence on The-Dream.
Love Letter is my favorite album of his, but it's not really essential R Kelly, because it's kind of him stepping away from craziness. In the mid 00s he was known for being a crazy person more than a musician, and the songs he was putting out were hilarious (though really good) songs like "Sexasaurus" and "Echo" (the latter is about fucking a girl until she yodels). On Love Letter, R was going back to the sound he's best at, which is smooth, quiet storm stuff with groovy beats that are easy to step to. And the lyrics aren't quite so freaky. It's just a really solid album that shows what a talented multi-instrumentalist, songwriter, and producer he is. No bizarre humor to hide his true skills.
Here are my two favorite songs from Love LetterJust Can't Get EnoughJust Like That
and just for the hell of it, here's one from 2004's "Happy People" that I like a lot.Weatherman