See all units’ health bars in real time in Age of Empires 2 HD

According to the developers, the game's multiplayer mode will not be compatible with the original:

I have the original Age of Empires 2. Can I play multiplayer matches with my friends who have the new HD version?

Age of Empires 2: HD Edition uses a different multiplayer service than the original version, so cross-platform matchmaking is not possible. You will need to have the same version as your friend in order to play together.

In the original game, you can only move up to 40 units.

In the HD version of the game, this number has indeed been updated. You can select and move up to 60 units at the same time. It used to be 200 in the public beta of the 2.4 patch, but it has been quickly lowered to 60. There is no real explanation for that, but main suspicions is about path finding being too complicated to calculate, while other think it could be because of the game balance itself.