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Well as you know there is a STEAM demo and a GOG demo, i noticed there had been a bit of filtering added on the STEAM page AND the ability to use grenades! but the GOG one hadn't been updated on my Galaxy. I also suffered occasional crashes. I decided to download the STEAM version just for curiosity.. Well, this is strange. It runs very well on STEAM (i also suffered keyboard lag on the GOG version, none on STEAM..) the filtering is brilliant, it's easier to see objects on the ground now, explosions have been added and the grenades (limited from previous version-only a couple) are spot-on.
Try and see if you notice any diference?