Hmmmm. Just off the top of my head:
Omaha Beach from Medal of Honor: Allied Assault. Will always be awesome.
The Heat-inspired bank heist mission from GTAIV. Makes me super excited for the heists in V.
As far as bosses go, pretty much all of Dark Souls.
05/10 - Septicflesh
05/16 - Anaal Nathrakh
05/17 - Aborted (?)
05/21 - 05/24 - MDF XIII
05/27 - Cryptopsy