So I have a crap video card Radeon HD 4200 512MB. So DX11 games are completely out of the question. They run like molasses. So I'm hoping that anyone may know some good games in that DX9 or DX10 range that are on Steam.

I'm playing War Thunder (in the Steam free to play section) at the moment, which I think is actually using D3D9.

Knights of the old Republic one and two are really good and don't require a beefy graphics card. Not sure if they're actually DX9 or so though.

Assassin's Creed I, II, Brotherhood, & Revelations

All Prince of Persia games

Burnout Paradise

Prototype

Devil May Cry 4

World In Conflict

Sonic Generations

Torchlight I & II

Mortal Kombat Komplete

...

List goes on. You can ask Wikipedia

Really if you know what the demanding games are to avoid, you can play about anything - on low to medium settings and at a reduced resolution.

I'm still going to take the unfavorable opinion though and say with a system like that, if you want to game, buy a PS4.