He made a good game.
He didn't make a good Diablo game.
Someone wrote this in another thread, and I believe it to be the most succinct and correct opinion I've ever read on the subject.
Jay Wilson was essentially handed a slightly rusty, slightly beaten up 1955 Corvette that he was supposed to restore to showroom quality (Diablo 2 LoD with YEARS of work put in on patches, fixes, and improvements).
Instead of hammering out some small dings while adding shine and polish to the great factory car already there, he decided to replace the bumpers and panels with custom models, strip the leather interior for his favorite mediocre fabric, gutted the dash board, threw out the floor mats, and added flame decals and a spoiler. Then he followed it up with a yellow-green with purple polka-dot paint job (Scrapped the skill and stat system, gave Diablo bewbs, updated the graphics but probably went overboard and now it's not dark enough. Also cut charms, runes, jewels, crafting sucks, there's no gold sink to help stabilize the economy).
For some reason, he decided to present the car as ready for the showroom with no wheels (no PvP, everyone moves rather slow), but promised everyone that attended the car show a month later via mail that the wheels are on the way - then had to text them and say, oops, wheels aren't on the way just yet (PvP blog/twitter thing).
And so there it sits in the showroom. It's pretty obvious that the car is a '55 Vette, but it's Jay Wilson's '55 Vette. All anyone wanted was that it look like a Chevy - the classic they all knew and loved, but with a shiny new paint job, no dings in the door, and some nice shiny new chrome on the wheels.
...dammit why doesn't this car have wheels?
This restored car is good. The engine works. You can drive it for days, and enjoy the ride. But it doesn't ride like you remember the 55 Chevy riding.
He made a good game...but not necessarily a good Diablo game.
Bear in mind that he had, what, roughly the same amount of time to develop D3 as D2 had a lifespan, and a SIGNIFICANTLY higher budget than Blizzard North had back then. Yet the end results is vastly inferior.