I would suggest autumn aurora if you want graphics upgrades without a heavy shift from the original game. That is for the original stalker game, call of Chernobyl.
Anomaly combines all 3 game worlds into one large world but it has it's own storyline and it has a lot of survival mechanics. Still, the graphics look amazing once you apply some model upgrades to the character models and the difficulty is highly customizable. I would recommend giving it a shot if you are bored and you have run through the original games again. Do a google search for the HD model packs and you will be surprised how well the game holds up with all of the modified assets from AA2, Anomaly, ect.