If the OP wants "serious games" (beyond Serious Sam, which is obviously the BEST suggestion) then maybe a proper ARG is for him/her.
Or you could check out the work of people like Jane McGonigal:
http://janemcgonigal.com/
No, I had a crush on her brain and enthusiasm first!
But seriously, people like her are writing some pretty important stuff and it's cooler than fuck.
Here's someone else doing something similar:
http://www.ted.com/talks/jennifer_pahlka_coding_a_better_government.html