I recreated my very first character -- a human warrior, because in the last-push alpha test I joined in 2004, there was no Horde -- and logged in. Immediately, I was surprised by how good the graphics actually looked, for being 15 year old textures-on-polygons. Warcraft's bright colors and cartoony aesthetic continue to this day, so all the increased resolution and better-contoured characters in Lordaeron don't really change the game's visual aesthetic.
However, that’s not the full extent of Blizzard’s announcement. The developer behind World of Warcraft Classic has also announced that it will release a closed beta test for chosen (note this word) players to participate in. The closed beta is meant to test Blizzard’s servers, which I’m guessing will be pretty full once the game actually releases. Blizzard hopes that this beta can prepare them for a smooth launch, since this is pretty big for World of Warcraft players.
Apparently a lot of the current World of Warcraft Classic closed beta testers are reporting things as bug that, well, simply aren't. There are enough of them, in fact, that Kalvax, the Classic community manager, posted a lengthy "Not a Bug" list on the forums. Some of the things that are actual features in the game include Tauren melee reach and hitboxes are larger than other races, Warrior health regen is working as intended and creature respawn rates are "much slower".