I'd say his current stuff lacks flavor, but during his prime- his delivery was top notch. In my mind, the biggest issue is longevity. He's just been in the game too long. We've heard him rap over 100s of beats. It's going to get old over time + his hunger just isn't the same (that's where the lack of flavor comes in).
Nas is the only other MC I can think of that is built of the same ilk; in that he drops a new album every couple of years spanning over decades. He's had his misses as well, but damn is he aging like wine. Most rappers have their 5–10-year peak, then drop music once in a blue moon.
As for whether or not he's one of the greats- everyone will have their opinion, but at the end of the day- he has a ton of respect among his peers. Kendrick has him top-5 ever, Cole has him borderline top-5, Rakim has him as one of the best ever, D Block has love for him, Method Man and Redman admire him, Chuck D f***s with him, Nas and Jay as well, etc...the list goes on and on crossing generations of rappers.
So, in my mind, regardless of what a few fans think, especially new generation fans who didn't experience his prime- he'll be viewed as one of the greats because he has the legacy + the game has a ton of respect for him. So, us internet heads can debate until we're blue in the face- it won't change the fact his legacy in the game will be that of ONE of the best to do it.