Diablo 3- Pretty much everything
Diablo 3 - the nemesis and gifting system is awesome
This. And although quoting lastplace after Omo already said everything may seem redundant, it emphasizes how great the game's mechanics are.
pause and being able to save and not start over from beginning everytime
This too. Especially when the save system preserves your location/progress as well, like being able to save in the middle of a dungeon without hitting a save point.
This is an older one, but I loved the sanity meter in Eternal Darkness. It was a really cool concept in where the lower your sanity was, the more the game would mess with you. I don't know if any game has tried to incorporate a similar system as the main draw to the game since then ...
IIRC, Call Of Cthulhu had something similar.
Skyrim.
This too. 100% truth here. Actually, Paul Tassi wrote about Skyrim a few days ago. Worth reading: The Solitude of 'Skyrim' Remains The Remedy For An Overly-Connected Age - Forbes
So, a few other things:
1. Bulletstorm's Skillshots. I will never get over that system. It was awesome.
2. The sheer volume of events in Forza 2, 3 and 4, Forza 2's parts customization, Forza 3's loyalty system for upgrades and the depth of the car customization system in 2, 3 and 4.
3. Borderlands' cel shaded graphics. For that matter, the aesthetic in Contrast, Transformer, Mirror's Edge, and a bunch of other games I'm forgetting but made my jaw drop. (Like that massive underground Dwemer area in Skyrim.)
I know I'm forgetting a TON more, but that's enough for now.