Well I have always maintained that Diablo was based on Gauntlet - running through areas killing monsters, opening chests and collecting potions and loot,but I suppose I can see your point. Hope its not a sign that the inventiveness of the team that made I and II has given way to lazy knicking stuff from other games.
Choo talkin' 'bout, Willis?
You want the D3 dev team to remain inventive and not nick things from other games whilst claiming (and I agree with you here) that Diablo was based on Gauntlet?
Gauntlet itself must surely be based on D&D.
There aren't many new ideas around these days and one can hardly claim that any form of dungeon crawling is innovative. Blizzard's strength is taking a proven concept, coming up with a compelling storyline, adding their own touches (I'll grant you that some of these could possibly be considered innovative) and making it better than similar products (subject to personal preference, of course).
If that involves adding their own take on fun ideas from other games then it's fine by me.
By the way, the mirror effect is also the Mage's signature level 80 spell in WotLK