About Metro 2033 (not the Redux version)

I do not own the game here but rather bought a disc many years ago and it had this text on the backside that informs me that it needs to be activated through a Steam account. This was my first bought game, and so far only installed one, that requires Steam.

So a couple of days ago when I wanted to play it again after a long hiatus the game complained about problems so I verified and repaired it and then it still refused to work and suggested reinstalling so I did and now the game works. So far so fine but:

After reinstalling, the game DOES NOT LOOK THE SAME ANYMORE :-O It is like someone smeared butter over my monitor :-( What has happened? I cannot post anything on Steam as I never paid a single cent there and you are not allowed to unless you pay them $5 I think it was. Kind of acceptable but annoying since I did pay for the game.