Greate Gameplay Core - Take it to the Next Level
Overall this was a great game and I really enjoyed playing it. I only found two flaws but neither were too major. First, moving a group around objects often resulted in units getting stuck rather than moving around them. There were ways to avoid this but it made it difficult to use tactics such as flanking quickly. Also, some of the bonuses, notably healing, seemed inconsistent.
With this framework in place, I think that you should focus on the presentation. The levels were fun but I stopped playing because they got repetitive. I would add some backstory and scenarios for each level so the players feel more attached to the game. Even simple things such as letting players name their units would help. A little variety in mission types could be fun too. Instead of just killing all of the enemy, how about acquiring a certain territory and holding it for a period of time, i.e. king of the hill. The possibilities are endless.
Next I would add some kind of statistics between levels and perhaps even medals for beating the game on easy, beating the game without any unit dieing, etc. This would help the replayability. If you add just some of these features I can see this being one of the premier flash games in the genre. Keep it up!