Amazon has a serious deal for Serious Sam fans with the Serious Sam Serious bundle. Seriously.
For $20 dollars you'll own the entirety of the Serious Sam games available - that's 6 games plus some DLC - all available digitally so you don't even have to put on any pants.
- Serious Sam 2
- Serious Sam 3: BFE
- Serious Sam Double D
- Serious Sam HD: The First Encounter
- Serious Sam HD: The Second Encounter - Legend of the Beast DLC
- Serious Sam HD: The Second Encounter
- Serious Sam: The Random Encounter
So I lied, the first Serious Sam game is missing in it's original form, but you do get the HD variety. Almost every game supports co-op except for DD and The Random Encounter. Go get it while the getting is good, and support Co-Optimus in the process!