So much for smooth!

[Nysard]

Those getting "Unable to validate game version"

simply flush your dns

Bring up CMD, ipconfig /flushdns

Worked for me

The other way of course is to wait until all the authenticating servers are updated to 2.4, either way should work.

Eidt: Realms have just started to come online now

[Nysard]

Aaaand stuck at 99% for hours now, yeah well, Shattered Universe, here we come

Try grabbing it from a mirror instead perhaps?

2.4 Patch Mirrors

[Erethas]

Hey, at least you could TRY to play. I didn't even have internet connection for two days now for no apparent reason.