3d can age well also, Warcraft III still looks better than most modern games, it might not have dynamic lightning, shadows, etc but the overall impression is just stunning.
Warcraft III is such a great example of how make sure the 3D isn't working against you, both from gameplay and visual perspective. The camera angle is always fixed which means they can optimize the way characters look from that particular angle, not like sims 3d where you can zoom in and around and end up looking at an untextured ceiling. This also makes it much easier to design the gameplay such as selection and control of characters because there is only one scenario to cater for, instead of twisting the camera to select a character behind a building/mountain you simply design the game so that characters can't be hidden behind mountains. Other 3d RTS games from that era(probably today as well) made the mistake of thinking we haz 3d!!!1 now the player should be able to move around everywhere which just can only end with infinite bad camera angles instead of one good one.
One of the main issues with 2D is the fixed resolution. If you can live with that, it's not bad. I actually played D2 again a few years ago and really enjoyed it. Same for Planescape Torment.
We are well past the point where it explicitly ages badly though. HL2 still looks pretty good IMO and that is past a decade old. A few years ago you couldn't say that about many decade old games.
No 3D game released now that doesn't look terrible to start with is going to look hideous against what-ever is modern in a decade's time - it won't look as good of course, there will various bits of flair/realism/detail/what-ever missing somewhere, and the uncanny valley and such effects will be more noticeable, but it'll be perfectly playable and if the game is good the lesser graphics won't make it any less good.
Going back to HL2, if you compare it to Bioshock Infinite you can see the improvements in technology over the years, but it sill just looks less refined, not bad, and the differences don't affect immersion much (I would argue that BSI is more immersive, but that is mainly due to the design improvements (the whole but: art, music, story, ...) and not really due to the graphical improvements on their own).
This hasn't stopped Mario 3D, Zelda: Ocarina of Time, or Final Fantasy VII from becoming classics, despite being some of the first games in the 3D space.
> That doesn't mean that it makes the games less enjoyable, necessarily, but certain art styles are just better at conveying timelessness.
However, that art style is not pixel art. I've gone back and tried to play some of the pixelated stars from the past - they don't age well on modern display devices. From their 40pt fonts, to their pixels which actually look worse on LCD monitors than they did on our old CRT TVs.
They are still classics, and frequently enjoyable, but in many ways they require a bit of context to understand why they were such classics.
I have a stash of bulky crt monitors and TVs for this reason. They are almost free nowadays.
That's why it's timeless.
The original DooM engine isn't based on billboarding.
> "...your field of view is strictly limited to a 2D plane, but the use of isomorphic projection and billboarding techniques are used to create depth"
That doesn't mean that it makes the games less enjoyable, necessarily, but certain art styles are just better at conveying timelessness.
At some point we'll probably reach a certain peak level of graphics that can simply be considered "good enough" for most purposes henceforth (Have we already?), but in general investing too much in graphics for production purposes over tech demos and research, is often shaky.