It's £13 on Steam. I haven't bought it. I was sceptical. There are already high resolution mods for AOE2, and it doesn't look like AOE2 HD adds much that these don't.
From what I've read, I was right. It seems extortionate to re-release a 14 year old game for £13 with no substantial improvements.
Also, as much as I loved building walls around my walls and spent many, many hours doing so ... I can't help but think that Civilization has probably ruined RTSs for me as being a bit shallow.
Civ 2 + 3 (+ Alpha Centuri) HD would be more interesting.