AB2012: Interesting. For all the recent attempts at making games look "new old school" (usually by dropping Minecraft textures into Unity 5 Engine, making the levels procedural then removing quicksave, none of which are really that accurate vs most 90's shooters engines), to me it's often that snappy, super-responsive of the old 90's engines that makes them
feel proper "old-school". It's a shame more devs don't do this. I'd happily pay for more high quality Doom MegaWAD's like a new "Final Doom". Or more "full campaign" Thief mods like another T2X in their original engines. For all the troubles with Night Dive's attempt, I'd be perfectly happy with a System Shock 1 remaster using the System Shock 2 engine too.
Well, if you want:
Thief/thief 2 mods:
http://www.komag.net/ (There was even dvds full from there at one point)
Thief 3, look at the dark mod:
http://www.thedarkmod.com/main/
It's now standalone and has a ton of missions
Doom:
https://www.doomworld.com/
Also, don't forget the project warlock came out recently and that is pretty good, played it all the way through and it's worth looking at. Looking forward to iron maiden also.