Depends on the feature and if they translate it to be warcrafty enough.
Loot goblins fit into world of warcraft and are a fun diablo feature. So thats a good idea!
Every spec they were unhappy with getting a no depth "charger, spender" diablo playstyle instead doesnt fit into the more complex and slower gameplay of WoW, so thats bad.
And so on.
There is no general problem with games taking good ideas from other games I think. As long as they arent doing the Ubisoft things, where every new generation of their main franchises loses some more of their identity and is slowly becoming a grey blob of "climb tower sandbox with facebook games with theme X tacked onto it".