The quality of animations for sure, as others have said. I love how the old system made your character have real inertia, leaning into turns, scraping up at quick stops etc.
I also miss some of the music, but hoping that they re-use some tracks. At the time I was so sick of hearing the Van Halen-esque battle music but it could be a cracking boss piece in 2.0. I also loved the meshing of the old Toto-Rak ambient/battle music and thought it was very cleverly done.
EDIT! To add one more thing, and this is something 2.0 will never (hopefully never, paradoxically) have in the same sense, was the feeling of approaching doom. The whole "world will end in X days unless we do something about it!" plot is used all the time, and no matter how well it is done we as an audience always knows that somehow it'll work out and things will be OK. Those months leading up to the end of 1.0 with Dalamud getting larger and larger each patch, coupled with the fact that we knew things were not going to be OK was an interesting feeling. Very unique, and gave us that feeling of helplessness that your character would be feeling too. The culmination of the fighting at the end (well OK, I got to play maybe 10 mins of it without dropping?) then watching the released scene afterwards left me feeling "Well, balls. We failed."
The last time the bad guys succeeded to that level was in 6!
Edited, Sep 28th 2013 7:28pm by Kordain
To endanger the soul endangers all,
when the soul is endangered it must become a Warrior.