I don't think Drake is among the greatest of all time (at least, yet - he needs more time to suck up to older rappers who are less good than him), but I do think he's pretty good. At least, he is better than many mainstream rappers out much, which doesn't say a whole lot, but at the same time he is good in his own right.
From a technical perspective, he usually delivers, and what I do like about him is that he often changes up his flow on different tracks so he isn't as predictable as other rappers.
Of course, he's not pure-rap and often dabbles a lot with pop and r&b, which is not to everyone's liking, but no doubt it courts the feminine audience, a big demographic to his success. So I judge him as a hybrid artist rather a straight-rap artist. In the same way, I wouldn't bash Eminem for not following the bling-bling ghetto formula that rappers like Rakim and Snoop Dogg set.
On that note, probably the biggest criticism against Drake is that he isn't gangster enough. He had a relatively privileged upbriging. However, I respect him for not trying to be a 'studio gangster' like so many rappers do. A large amount of rappers exaggerate the roughness of their upbringings (especially the ones who rap about the hood) so at least Drake is honest.
I'm not painting everyone on here in this light, but many Hopsin/TechN9ne/Eminem fans think that rappers who don't rap 20 multi's per minute are garbage, and that's just closed-minded, IMO.