Before R&B was commercialized and mixed with hip-hop, it was music of the likes of Marvin Gaye, The Isley Brothers, Phyllis Hyman, Minnie Rippington, and more current examples India Arie, Jill Scott, Maxwell, etc. Modern R&B like Jill Scott and Maxwell is usually called "Neo-Soul" which is considered a bastardized term for R&B. Honestly, many artists considered neo-soul (i.e. Dwele, Musiq Soulchild) are actually real modern R&B.
While authentic R&B contains deep lyrics, especially Afrocentric experiences of love, relationships, cultures, politics, etc, mainstream "R&B" tends to focus on sappy love themes, sex, and hip-hop lifestyles.
Alicia Keys, Bobby Valentino, Mariah Carey, and Keyshia Cole are NOT authentic modern versions of R&B but instead commercialized types of R&B/hip-hop made to please the mainstream palate.
It usually has mellow or laid back beats and rhytms to it, and quality vocals for the most part.
2) Hey let's listen to some Isley Bros., some good 70's R&B!
3) Hey let's listen to some various artists, true 80's R&B!
4) Hey how about some Aaliyah for some great 90's R&B!
5) Hey how about some Foxy Brown for some good modern R&B!
Today's popular music, like Destiny's Child and Mariah Carey, is actually NOT R&B. It's hip-hop and some nuthead decided to call it R&B. The real R&B artists are very annoyed by this.
Now R&B is this over saturated stuff that only have about 3 artists that matter - t pain, akon, and the dream and they sing about the same thing.
R&B now - Shawty damn she's fly, damn she's hot, I wanna fuck her all night long AYYYYYY
Decent current R&B - Mariah Carey, Amerie, Charlie Wilson, etc.