I know a lot of people hanging out here enjoy the old-school gaming style (non 3D gaming).
A particular favorite game genere of mine was a 2D shooter with a shop that allows you to upgrade and customize your ship. Previously Tyrian 2000 was the best example of such a game.
However now there is
Jet's and Guns' Gold!
If you loved Tyrian 2000 and don't mind side scrolling vs top scrolling then you must check out this game.
http://jng.rakeingrass.com/