When I read the thread title I thought that "criminally" meant "disappointing due to either malpractice or active intent". In this case my answer is straight: D&D 4E. However the
enthusiastic reviews and the specific kind of hype that surrounded it were the very first signs that it was going to be stupid, so it is not an answer to your question (*).
Hmmmm... strange... the only game that qualifies, for me, is Risk - which is not an RPG at all, of course, but which is up there with Monopoly in popularity and still makes my nose bleed with boredom and me put baffled question marks around his success.
Partially GURPS 3E, which I actually loved and played a lot, but that suffered from fatal idiosyncrasies that jumped on you on the most unexpected moments and had to be house-ruled to hell before the game became fun again.
And partially MERP: great fluff (Moria!), but I.C.E. choice of RM Lite for the crunch was a disgrace.
Pathfinder, now that I think about it. Which is a bit of a paradox, since I'm happy that 3.5E lives on, viva Pathfinder and stuff. But they didn't really fixed the problems of the earlier game, and the Pathfinder
unfanboys agree that "The biggest open beta-testing evah'" was a little bit a total farce. At the end the best solution, if one has 3.5E on the shelf, is to download the free conversion booklet and maybe buy the PDF of the main book, integrate the best bits (like the skills' streamlining, the streamlining of combat maneuvers and the new cantrips rules) and live happily ever after.
(*) I still consider the $$$s I spent for the two FR books - bought in Washington D.C. while vacationing there, read with increasing disbelief over a week, and left in a bin at the airport - as money lost due to malpractice, though.