Well there is a difference between mainstream rap style, and mainstream music

mainstream rap style consists of shallow, short verses and usually relatively unskilled rapping in between a lot of chorus. Not usually very deep, topics include and are limited to money, 'bitches', cars, narcotics. Appeals to the young male/young girl demographic(see: idiots). This type of music appears on the radio in regular intervals, and has a broad audience (hence the main stream)
:)
Examples would be:
Soulja Boi
Young Jeezy (although he has some hard tracks underneath it all)
Akon
Three Six Mafia (post- when the smoke clears)
Eminem (post- Encore)
Fat Joe (post- Jealous ones envy)
lil Wayne

If any one would like to argue about the actual lyrical skills of any of these artists sans Eminem or Joe, I would like to hear it. always open to hear the other side from an intelligent perspective.

I'm not saying relapse isn't mainstream
and its not always about pure lyrical content, even if someone sneaks in clever verses in between a gimmicky chorus that dominates the song, then it doesn't matter. BA DOING DOING DOINGGGGG
His topic is irrelevant at that point anyway, its execution that matters.

Wiz Khalifa's content is sorely lacking, it is literally the same redundant content in just about every song, but he executes it so well that its not really an issue.

But I think this is all discussion for an entirely different thread, so I digress

Mainstream is what's popular. Gilgamesh, stop being a fucking poseur. If you like his earlier stuff better, whoop-de-fucking-doo. It doesn't mean his later stuff has less integrity or that people who like it are somehow wrong. Your cringeworthy passive aggressive comments - e.g. "it is literally the same redundant content in just about every song, but he executes it so well that its not really an issue", kind of akin to saying "wow you pull off being fat really well" - are the whiniest shit I have ever seen in a hip hop discussion. You are about as hip hop as fucking Carrot Top up the arse.

Also, Shadows on the Sun is an awesome album.

I would like to add Its Dark and Hell is Hot by DMX