There is Wine like mentioned above. I’ve heard that HL2 can run on wine smoothly (in windowed mode). My Ubuntu PC could handle HL2 with everything on low but my graphics card is older and Ubuntu no longer supports the driver for it. Which means no 3D games for me . But in other words get Ubuntu or a similar linux distro if you want. If you’re satusified with Windows 7 stay there. Windows 7 imo has much better features than Ubuntu does.
I love Ubuntu. The only thing i use Windows for is gaming. Check out this, and this might convince you. It’s special effects for linux only called compiz fusion. https://www.youtube.com/watch?v=E4Fbk52Mk1w