There are two ways to answer the question asked in the title.
1. He is a professional rapper, having been one for over a decade, and his professional rappings are quite proficient and popular. Compared to the average person — or, even better, compared to me when I attempt to rap (which often occurs when drunk and eating Thai-style fried rice) — he is great at putting sentences that happen to rhyme at the conclusion of each line together and rapping them in a coherent manner over a background musical accompaniment. The distance in quality between him rapping and you rapping is the distance between a Chick-fil-A spicy chicken sandwich and you attempting to make a spicy chicken sandwich by catching a live chicken and attempting to sandwich him between two slices of Wonder Bread. So yes, he is good at rapping. This is an objective and inarguable truth.
2. Objectively, Rick Ross's level of goodness (or perhaps even greatness) is difficult to assess and quantify, because the answer is inextricably dependent on A) how you define quality in this context and B) how you personally feel about Rick Ross, the person who raps. That said, I will attempt to answer this as best I can. And the answer is I don't know.
I've been listening to rap music for roughly 30 years now. The first cassette I owned was LL Cool J's I'm Bad. The first record was Public Enemy's It Takes a Nation of Millions to Hold Us Back. And in between those purchases and my latest download (Drake's pretentiously kaleidoscopic More Life), I've listened to, studied, debated, and argued about every rap artist worth listening to, studying, debating, and arguing about. Which is why I have no reservations with saying that Rick Ross is one of the most gifted rappers ever. Not one of the five or 10 best (more on that later) but one of the five or 10 most talented. If a checklist existed listing every desirable quality a rapper could possess — a Zillow or Trulia for MCs — he'd fill every box.
It starts, of course, with his voice, which is one of hip-hop's greatest and most recognizable. It's deep and baritone and thunderous without being cacophonous and distracting. And syrupy without being saccharin. He wields it like an instrument; enunciating and resonating without seeming to need to put much effort into either. Even his ad-libs and grunts have meaning. Or, at least, seem to have meaning. He could say "I went to the store; got a bucket to eat" and grunt and leave you convinced that God just descended from the Heavens to order a two piece and a biscuit. He also comes equipped with an embarrassingly effortless flow that makes him impervious to suffocation. Even the best rappers occasionally get swallowed by good production. But aside from Biggie, Rozay is the only rapper who never seems to get overpowered by the beat. When he's on a song, he makes it his.
Perhaps the best example of this occurs on "Lord Knows" — which A) many people consider to be Drake's best collection of verses ever (personally, I'd go with "6PM in New York") and B) is one of the best and most ambitious tracks ever from Just Blaze, one of the best hip-hop producers ever. To his credit, Drake acquits himself quite well on the beat. But his verses are accompanied by a strain of insecurity. You listen to him and you know that he is trying very, very, very, very hard to kill it and not get killed by it. But when it's Ross's turn to spit, the difference in confidence and presence is palpable. It's almost as if someone said "we need to get a grown-up on this song." And then a grown-up showed up, and did in 45 seconds what Drake couldn't do in three and a half minutes.
(Seriously, you listen to that song and start thinking the face Drake's making on the album cover is the face he made after comparing his verse to Rozay's.)
And, while Ross's subject matter is infamous for lacking variation, there's enough diversity and creativity within his writing and his concepts to make the same subjects — usually limited to Bentleys, kilos, bitches, bitch niggas, and regrets — remain entertaining. He's consistent and reliable without being mundane and boring.
So why, when asking myself if he's a good rapper, was my answer "I don't know" instead of the clear resounding "Yes" it would seem to be? Well, the "I don't know" stems from a factor I try to shy away from when judging and assessing rappers. But, in this context and with this particular rapper and this particular question, it's too important to ignore: Record Sales.
In 11 years, Rick Ross has released nine solo and three collaborative albums. Of those, Port of Miami is the only one to reach platinum status, and that happened 10 years after it was released. Sales usually are not an effective rubric when assessing quality, as the only thing they measure is a very specific type of popularity and marketability. (Hi Nicki!) But his music is known for its lushness and luxuriousness; you listen to him, and not only do you believe he's a billionaire, he makes you feel like you're a billionaire too. When my Spotify playlist happened upon Rozay and I happened to be driving, my Charger morphed into a Maybach.
Also, each album is practically a who's who of Niggas With Islands And Shit. And is released with the pomp and circumstance of a royal engagement party. Teflon Don alone featured John Legend, Jay Z, Cee-lo, T.I., Jadakiss, Erykah Badu, Diddy, Kanye, Ne-Yo, Trey Songz, Drake, Gucci Mane, Styles P, Chrisette Michele, and Raphael Saadiq. That's a shitton of rich niggas with extensive Wikipedia pages. And he shamelessly shoehorns formulaic songs on these albums; tracks whose main objective is to hopefully give said albums the best possible chance at selling millions of copies. He has attempted, 12 times now, to create blockbusters, not masterpieces, and he's failed each time. It's Michael Bay's sensibility with Wes Anderson's box office.
And, it can not be ignored that while most trap rap offers at least a plausible fabrication of hood realities — you know that the person rapping probably doesn't do what he raps about anymore but has at some point in the past — Rick Ross is transparently counterfeit. Not only did he not sell drugs, he detained people who sold them. Which, in a macro sense, isn't a bad thing. It's better to lock criminals up than to do crimes and shit, I guess. But in the micro world of rap music, perhaps this anti-meta lack of authenticity is an invisible albatross holding him back.
That said, I generally like his albums. Even sometimes more than albums I recognize as objectively better. (I've probably listened to God Forgives I Don't three times as much as To Pimp A Butterfly, and I believe Rich Forever is the best mixtape ever.) So I remain tempted to answer "Yes! Definitely! Rick Ross is absolutely a great rapper!" even while knowing I might be wrong.
But just as I know that the 10th Rick Ross solo album, whenever it's released, won't be much different than the first, I know that some time this week, I'll be riding around Pittsburgh listening to Rather You Than Me. And I'll feel like a billionaire while doing it. And the answer to my question won't matter.