Was Diablo 3 a bad game? No.
Was it the best ARPG of all time? Subjective, but I don't think so. I personally thought it was okay-- and it HAS improved vastly since launch-- but there are two major difficulty related flaws that make it not worth it to me. (This is actually endemic to the Diablo series, not particular to 3-- it's the same reason why I never really got into 2 beyond a single playthrough.) My preferred difficulty is Hell-- the first two are too easy, Inferno requires too much time (or money) spent gearing to be worth it to me. And I can't play any other classes without spending hours leveling through way too easy content AGAIN. I play games to have fun, not to spend hours and hours grinding boring content to earn the right to actually have fun. If it were offline I'd just hack in a level 50 character in reasonable, difficulty appropriate gear and go for it, but that's obviously not an option. (I actually am not at all grouchy about the online only part-- it actually makes sense to have an in-game money-based trading system given how common it was in D2, and the little bits going to support the servers aren't a big deal.)
While it's not perfect, either, I found Torchlight 2 to be more conducive to just loading up the game and HAVING FUN without having to jump through hoops first-- I can just pick whichever difficulty I want from the start, on whichever class I want. If I'm not happy with how the game plays, there are mods.
Now, Sid Meier's Alpha Centauri is the best computer game of all time.
There's a mod made by Runic themselves that adds respecs to the game. Using it will mark the character as a character played in modded games. But if you like to try different specs, who cares? It's your game, play it the way that's most fun to you!