This is partly a self introduction (although my purpose may be inferred from my glut of other sudden posts having just found this board and hopefully i'm not considered spamming - each topic stands on it's own and I fear will not be seen by those most knowledgeable if it lacks it's own topic) and partly a request for more information...

I am trying to track down and eventually create a canonical list of all of the "dead branches" of historical gaming if you will. By which I mean when something started to branch off in a new direction, actually give a HIGHER quality experience for that time or at least for a specific game, but then since that direction was abandoned or usurped by other technologies, the "Best gaming experience" or even sometimes just a uniquely different experience for that game is no longer possible on modern new hardware, even with emulation.

For instance as near as I can tell, if you emulate the Sega Genesis, you get a higher quality experience than is even possible with the best modded hardware Sega Genesis. Having modern DVI out on your computer, the interpolation hq3x scaler options and similar combined with what seems to be 100% compatibility and no rendering errors mean that one doesn't really need a Sega Genesis strictly speaking to get the best experience, unless you just enjoy playing on hardware. I'm not aware of the sound lacking or being better on hardware - it sounds like a genesis to me/a good emulation of the chip, if others have disagreed you can share examples or references though.

Emulating the PC does NOT seem to be the same. There are many games which run perfectly on a modern Windows 7 system given a couple of patches and user hacks perhaps. Their quality is as high as possible because they didn't use anything unique anyways. Ie - something using EAX 1.0 still works fine on a modern Xfi card. My sole interest is on the hardware that this does NOT apply for - either there is no emulation/compatibility, lower quality emulation than real hardware, or something else that makes having the physical hardware of the time better or at least unique.

Video, sound, and game controllers are what covers this. (I can't think of any fourth category, can you? 😜) For video, the early windows 95 era had proprietary 3d API's which either gave a better or at least a unique experience. For instance GLIDE for Need for Speed 2se/3/4 was vastly superior to DirectX and OpenGL versions. However modern GLIDE wrappers give a flawless or even better than Voodoo 5 6000 level experience by what I can tell so that 'branch' is now rectified. DOSBOX works great for emulating most games and most hardware. But it's not always the case, and please help add to my list both of games and hardware:

VIDEO: There were other nonGLIDE API's such as the PowerVR series. By what I understand Mechwarrior 2 supported it and it looked prettier than what can be obtained on DX/OGL hardware. It also supported GLIDE but with a mixed experience. (missing textures and such) There were of course dead ends that belonged that way - by what i'm aware of there was nothing that used S3 Virge acceleration which looked better in any way - the goal here isn't different, but better, at least in some way, than what a modern PC can play it as. Likewise I think the ATI Rage Pro had some proprietary API that was basically considered crap... whereas the S3 cards were often a mixed bag sometimes better in some ways and worse in others... are there other games which supported some proprietary API which gave a better experience when using it?
ATI Radeon 8500 TruForm tesselation, supported in games like Morrowind 3, Return to Castle Wolfenstein, Serious Sam. It was either "much better" or mixed results (balloon weapons in Serious Sam) due to poor implementation, and as far as I know the feature was dropped/no longer enabled in both later drivers (disabled for existing cards) and later hardware (not supported in any form as of X1300 and later... perhaps it's only a driver disable though/could still be implemented?)
Nvidia GF3 supposedly had a similar tesselation system which was removed from future cards... was it ever supported by ANY game? I can't find any reference suggesting it was. 🙁
Voodoo 5 5500 T-buffer and such - I cannot find any evidence whether this (and some other enhancement) was ever supported in any game. I believe there is a Quake 3 motion blur patch supporting it... whether that patch is supported by the GLIDE wrappers I do not know because other than the Q3 patch I can't find any evidence any game used it at all.

HEAD MOUNTED DISPLAYS definately qualify as video as an aside. 😀 I seem to remember something about Terminal Velocity or Unreal classic supporting HMD's in some special option page? Does anyone know more than my foggy memory? 😜

3D GLASSES not compatible with modern systems. If it runs on Nvidia Stereo it doesn't need mentioning... were there dedicated 3d glasses supported by games that you are aware of?

SOUND is another big one. Both A3D and Sensaura were superior to Creative then (possibly even now according to some) and were supported in games like Half Life, Unreal and Thief the Dark Project. Playing with such audio is clearly a superior experience to any Xfi as far as I know. (although Xfi bought out Sensaura's technology and apparently included many of the things in Xfi, I don't think they changed the HRTF which is what it really had so vastly superior, and my guess is that running TDP on an Xfi system will give crappy Creative type HRTF instead of what it could do on A3D/Sensaura) The Adlib Gold is another card that apparently does not emulate in DOSBOX to quality equalling what hardware will do - although only used exceptionally in two games - Dune and KGB that I know of, other implementations were either not so spectacular or fairly minor improvements over what does emulate in DOSBOX.
What about OPL4 cards, did anything support them for PC gaming? Were there any other systems (Roland MT32 for instance) where actual hardware might give a superior experience, at least with certain games, than what DOSBOX can do? (I don't know if there have been complaints about MT32 emulation quality, just Adlib Gold that i'd heard of)

CONTROLLERS: I started a separate thread on this, in varying eras there have been unique controllers introduced that were supported at the time, but not anymore. Some no longer run (I believe some of the Act Labs flightstick hardware wont run on faster than 300mhz PC's due to some timing issue, for gameports), some used mixes of gameports and MIDI, or gameports and keyboard ports, and obviously if you want the "ultimate" experience you either need to have the controller in question hooked to a modern PC, or possibly hooked to a retro PC if a modern one will not even run it.

Please expand to my above notes with anything you know on the subject. 😀