All you have to do to win the game is play your cards right. If you buy all the bombs before anything else, the enemies seem easy. I only used one unit for most of the game on one specific row, knight on top row, spearman takes on the middle row, and wizard on bottom. To easily win each fight, you upgrade a specific attribute to the unit assigned to that row. The game was fun, the first time I played it, the lag was just too much, so I switched to a different browser. I found the final boss to be easy, since my spearman was fully upgraded, and I had everything purchased from the shop, the final boss just didn't seem like a big deal. Unfortunately for me, the Bitter Bit Battle Badge is bugged. So, I'd say it's a good game, but it has it's downfalls, I'd rate it an 8/10.
Whenever you get hit while winning a level, it counts as a hit. So imagine this, I have one hit till death, I win the level, and then an enemy hits me. I find this unfair and frustrating.