The original Doom 3, released in 2004, is no longer available on Steam unless players buy it as part of the Super id Software Pack, which includes 24 other items for $99.
Searches show that until Oct. 10 of this year the game was still available on Steam as a standalone purchase for $20, but this has since been replaced by Doom 3: BFG Edition, which was released on Oct. 15 and costs $29.99.
Steam users took the forums to complain about the move because the BFG Edition of the game has reportedly experienced problems with performance and does not support mods.
A Bethesda spokesperson told Eurogamer: "We do realise that there are fans that would like to purchase the original version of the game, and we're looking into options for them. When there's new info to share, we'll let everyone know."