It's an established tradition that whenever a new World of Warcraft expansion comes out, some classic dungeons get a redesign. After Scholomance and The Scarlet Monastery it's time for a new Upper Blackrock Spire (UBRS), an awesome old dungeon that — among other things — became famous for Leeeeeeeroy Jenkins.
Now that people have access to the beta and UBRS as a level 100 instance, we can finally see all the changes. Sadly the whelps and all the Leeeeroy Jenkins stuff is gone (although if you watch carefully, around 9:40 in the first clip you can see the dead body of someone familiar in the Rookery).
Also, UBRS was famous for being unforgiving and being a bit more complex even in the vanilla days. If you weren't careful you could end up easily in Lower Blackrock Spire, the other wing of the Blackrock Spire, by accident. Now this seems to be gone as well.
Here's a walkthrough video, put together by AdriaCraft.
Also here's Method, one of the top guilds in WoW, going through the re-designed dungeon.