I can't believe i'm saying this but...
Doom 3: BFG Edition well okay Doom 3 in general.
I'll go out in my way to say that I DO NOT dislike Doom 3 in general even though its obviously my least favorite within the series, and in this context, "least favorite" simply means within the bottom but is I still like regardless. Having played Doom 3 from the base game and down to the BFG Edition did make me appreciate the game in a better light.
Doom 3 was a game i had a lot of complains about mainly due to the rather bullocks Flashlight system in the original base game, which was fixed in the further editions of said game. Of course while Doom 3 was a huge departure from the classic formula that we loved, and the form that was resurrected in the 2016 reboot, what I did like about Doom 3 was it being a different entity altogether. For some reason, it was a game of its down and the way that the game uses lighting as part of the atmosphere was quite well done. The graphics of Doom 3 thanks to that lovely IDTech4 engine still holds up to today's standards considering that game and graphics engine is already more than a decade old.
Now for the gameplay, it is a lot slower paced, perhaps it is the slowest of all the mainline Doom games thanks to it having a semi-survival horror approach especially in the earlier levels. Though once you do get further in the game, the action does start to pick itself up and the game gets more action packed. Also, of all the mainline Doom games, Doom 3 does have the most bosses, and some of these boss battles as far as FPS standards go (and excluding Doom 2016's boss fights because those are way too good as a baseline), the Boss battles in Doom 3 are quite well done. Not to mention that there are some pretty interesting monsters in said game that could have made its way in Doom 2016 (maybe in the sequel to the Reboot ;) ).
But yeah, shoving aside any Doom 3 hate for abandoning the series' run-n-gun-rip-n-tear formula, Doom 3 still has some of its quirks that make it a unique and still worthy entry in the series. As far as aging well, it definitely holds up. Its one of those games that greatly mixes the classic FPS formula with a bit of the Survival Horror mix, something that a couple of games can be like in the near future.