Original version did have some resolution problems if I remember right. Don't know about the steam version but it was fixed later on with patch. The real reason for bad reviews could be anything but what I remember of playing non-steam version:
-The game is a bit different from previous games (Aftershock and Aftermath)
-Combat isn't so forgiving if you make wrong decisions
-The UI doesn't tell you everything or hides things (I remember people complaining about certain thing in game which wasn't explained clearly so one couldn't know how it happened, can't tell more because of spoilers)
-Style of graphics was changed a lot from previous ones and the sound acting can be even hilariously bad.

I don't say that UFO: Afterlight is a bad game. It only lacks some polishing and could have been grittier and darker as the previous titles were in their style. I still enjoyed playing the game through I recommend everyone to ry if they are interested of earlier X-Com games and/or UFO series.