We can bring back the old bump/normal maps, (to an extent, the specular maps) as well as the shaders and various other effects that were used in 1.23.
What /can't/ be brought back is the way lighting/shadows were rendered in the old engine. The method they were using was capable of casting a seemingly perfect shadow but underperformed in generating an even result overall due to the excessive volume of computation time required to use this method, but on the plus side provided a perfect light source for all the bump/normal/specular maps that were used.
The downside of this old way of rendering the scene proved VERY expensive and required a pretty beefy system to even run it at the "halfway" mark let alone the full-hog.
What is normal mapping?
Almost every game you play probably uses this method, where a higher detail model is created then a colour coded 'map' of the detail is made and applied to a lower-detailed object (shown below), which gives the illusion that the lower detailed object has more detail based on the light sources in the scene.
Now, where the comparison between 1.0 > ARR here is the actual resolution of the textures used for bump maps and diffuse (AKA flat image) textures, is considerably lower where finite details are lost which when it comes to bump maps REALLY shows.
ARR
1.0
An example of 1.0 > ARR comparison is something like muscle where there was definition before, only the outline/shadow remains, you can see clearly below the shape is retained but the nice finite details of the neck, pectoral muscles and arms are completely.
1.0 gained most of its ""beauty"" through textures like these as well as its attention to detail for cut scenes and animations.
DO NOT mistake 1.0s lighting/shadows as "something to be missed", it really isn't, the actual detail you enjoyed wasn't found in this lightning/rendering system for the most part, another effect you don't see in ARR is 'Bloom'.
Bloom is an effect that saturates and adds a 'hazy' light effect to the scene which if balanced incorrectly can look too bright and tacky, where-as in 1.0 you'd have noticed they blended bloom into the game so that it had the intended effect without it overkilling everything else.
Square Enix reasoning behind this 'change of heart';
Lower resolution textures use considerably less memory, the current lightning model their using (Deffered Rendering) uses a lot less computation time (and memory) also, broadening the games audience.
1.0's problem was, half of the people couldn't even run the game which affected their enjoyment (even more so than the convoluted systems to play 1.0 on release) so it's a no brainer that Square Enix dummed down the requirements.
Now, for the lightning/shadow rendering (Deffered Rendering) in ARR, this is very scalable which is why its become so popular to use in games as of recent, where the resolution of the shadows being casted from objects in the scene can be adjusted as the developer sees fit, the only problem with adjusting this is increasing this further and futher will obviously sky-rocket the computation time required to draw the scene which is why we have a limit of 2048 currently.
Animations
Animations in 1.0 were fantastic, no doubt about it mainly due to the fact that they used 'inertia', there was a gradual /beginning > animation > end/ to every animation; walking, running, attacking or casting you'd always begin and end the animation flawlessly, as a result of this an animation-lock was added in (if you remember).
Animation Lock for those who don't know, locked you into whatever position you were in whilst you were casting/attacking making it almost impossible to dodge any AOEs or attacks once you began casting, leaving you with only a few seconds to either cancel the cast and them move, or finish and moved. This required at times precise timing and either proved a fun challenge or just; "Oh my god, animation lock erupted me again...sorry guys!".
As a result reworking the animations for 2.0 resulted in quicker movement where inertia simply wasn't possible anymore, so we now have a choppier (and sloppier) look to the animation. But compared to most MMOs the animations we DO have now are fantastic, just not as great as before.