If I had to pick a few, I'd start with Leoric's Undying passive (haunt the battlefield as a ghost after you are taken down), Cho'Gall's 2-player gimmick (2 players controlling one body), and Ragnaros's Molten Core (take over a tower or ruin to become a huge raid boss).
Which ones would you like to see? And no flaming/bashing HotS, okay?
Cocho2 votesa working death recap
darkdill1 votesAgreed. League's DR is an eyesore, but what does Riot say? "Not worth the time."
Rewt1 votesMovement Quing. Please. ffs. Its a mechanic that I use constantly and love. Hots is build on the SC2 engine and literally copy pasted the movement que mechanic and Its amazing.
As for character mechanics..... probably something like abathur in the support role would be interesting. Maybe set it up like the Kindred mark so that you have to wait before switching players but that idea of a Solo XP bot laner who can get assistance from a distant support sounds very intersting.
OurLestrade1 votesIllidan's global gap closing stun thingie, which is very fun to deal with as Sylvanas. ... These aren't repressed HotS memories or anything...
darkdill1 votesNocturne kinda does that. It's just not global because "TOXIC! IMBA! WRONG!" says Riot.