I'm going to write about this game until everyone I know has played it. I know I've posted about it before but seriously (that's right, it's serious) this is a must-play for anyone.
Yes it's retro, yes it's a platformer, yes the screen-res is low (unless you've bought the wii-ware version) and yes you do get a gun.
So yeah it's like mario (it's not like mario) and you have a gun (as previously stated) and there's a plot (rather than just a "story") with interesting characters (rather than a bunch of evil dinosaurs) and, well there's hours of gameplay here as demonstrated by this fan trailer:
Everything else you need to know, including download links, can be found at this site here.
Thus ends my "week" of concentrating on free games. I think I'll have another theme week soon though...