Time Lock Expansion
Basically, they started a new server at T5 (lvl 50 cap), and vote each month to open the next expansion, requiring a 2/3 yes vote to unlock.
This isn't like they took original code though and re-released it. The game mostly runs on the same system as the current servers, though some things are restricted - like no adornments yet and only dps and haste buff blue stats work atm. It is not as difficult as the original game, but you get to mostly get the feel of the old times. If you are a hardcore purist, you will be disappointed, but if you used to like the game up until SF or something like that, then you may get a couple years of good nostalgia out of it.
It does require all-access sub to play, but honestly, I would rather play old eq2 than most of the other stuff I have tried these past couple years.