Have to finish stalker to play the expansions?

Just curious....was thinking about getting Call of Pripyat on sale but I never finished the original.

I don't own clear sky either..

YOu don't have to, but it's a good idea to finish Shadow of Chernobyl before you start Call of Pripyat. There's nothing all that important you'll miss by not finishing SoC, but you'll miss references and the overall story. Clear Sky is a prequel to SoC and doesn't really connect with SoC as much as CoP does. I'd still recommend playing them in the right order of SoC, CS, CoP.

Are there any graphic mods that might make it less ugly?

A bunch. The most popular one being the Complete 2009 mod for SoC.

SoC Complete Mod

There are also Complete mods for Clear Sky and Call of Pripyat as well.

Awesome ty