As a 40-something year old guy with probably 100 rap/hip hop songs in my library (90 of them are from 1986-1992), I have to wonder "What makes a good rapper"?
I don't know a good rapper from a bad rapper, but I know a song that catches my ear and I am down with O.P.P. and I like to do the Wild Thing, sippin' on gin and juice. Word to your mother.
There's a lot that goes into making a good rapper. The biggest one that most rappers now days are missing is lyricism. It's gotten so bad that some people thing Lil Wayne is a great lyricist even though he is average at best. Other attributes include "mic presence" (how well the rappers voice sounds over a beat), breath control, rhyme schemes, word play (especially metaphors, alliteration, and double entendres), and flow which combines a lot of things such as where words are emphasized, how the rhymes are emphasized, how the rapper interprets the beat, etc. Beyond that writing skills are also very important.
Some people seem to irrationally hate rap and have very inaccurate beliefs about it. A lot of people think writing rap lyrics is easy (for example someone may make up really weak gangsta rap lyrics). I'll give an example of "extreme lyricism" starting with Eminem.
Since I'm in a position to talk to these kids and they listen
I ain't no politician but I'll kick it with em a minute
Cause, see, they call me a menace and if the shoe fits I'll wear it
But if it don't, then y'all'll swallow the truth, grin and bear it
Now who's the king of these rude, ludicrous, lucrative lyrics
Who could inherit the title, put the youth in hysterics
Using his music to steer it, sharing his views and his merits
But there's a huge interference: they're saying you shouldn't hear it
Maybe it's hatred I spew, maybe it's food for the spirit
Maybe it's beautiful music I made for you to just cherish
But I'm debated, disputed, hated and viewed in America
As a motherfu**in' drug addict, like you didn't experiment, nah nah
That's when you start to stare at who's in the mirror
And see yourself as a kid again, and you get embarrassed
The mainstream has been largely watered down and simplified, but the underground has tons of talented rappers such as Aesop Rock. Aesop Rock is a very abstract writer and has extremely complex lyrics:
It was less an act of hubris
More a lonely hearts club at the helm ofa magic bullet
Away on a relentless bid for rarefied inertia
Rattletrap forks married to the patchy terra firma Ursa Minor getting warmer
I crowbar into the pecking order
The dreck between the whores and Betty Ford-ers