AI is bad on both sides, controls need work
Well, that was fun like shooting fish in a barrel is fun, kind of like the AI on the first Warcraft. There was never any incentive to get any units besides cannon, their lack of speed was never an issue, and their range and damage made all other units obsolete.
The controls were frustrating, as has been stated previously the auto attack of your units overrides any command you give them, which means it is impossible to prioritize targets or retreat. This ends up not mattering due to the imbalance of units, if you have 9 cannons that kill everything, your units stupid AI turns out to be of little consequence.
Grouping was also a problem, the inability to set custom groups hurts games like this a lot. You chose to instead give a number to all of a certain type of unit, though this meant that you couldn't have groups of mixed units attacking two different areas and expect to be able to control them (again, with the AI, you couldn't really control them anyway). And somehow it was deemed unnecessary to give the general a quick select button? Custom groups would solve all of these issues.
It's not all negative though, the ability to set a custom path was a very nice touch. It's actually surprising you don't see that option more often.
Maybe you could set it so that if you hold down control or shift or something when you issue a command that command will take priority until the unit completes it (gets to the location or the unit it is attacking dies) or is given another command. I think that was used in another RTS flash game on Newgrounds somewhere, Battlegrounds, I think. That would solve a lot of reviewers issues.