nice iniative for making a flash version. i suggest a custom cursor ( human glove ) that can change depending the action taken on a unit etc.
you could also make the navigation easier by adding stop, attack attacks. the footman could gather gold, and he become invisible when he was heading to the town hall.
For each units, there could be a reason explaining why you cant buy a certain unit, telling what prerequeristies you need ( lumber mill, keep.. ) so you're less confused.
for a better play, there could also be a background music (you can fetch it out war3), interesting terrain art (might be complicated, but atleast it would be better than a bland yellow), a faster fps.
the terrain could've used rivers, mountains, and perhaps rescuable units for the hell of it.
this game have already a rather good score ( it's near 4 ), but it could easily climb more by inserting additionnal emphazis on the gameplay. war2 is a historical 2d game, and it do deserve good tributes :)