this is a great game, very enjoyable. I'm not sure the last level (3-6) can be won on the hardest setting without the premier content, but all other levels are balanced and fun. Barely any grind, except for the last level. I think I would need to grind quite a bit of money in order to beat the last level without a commander. I've maxed out all of my units except the healer and the commander (which I don't have since it is premium). But, overall, very fun.
This is a really great game. I came for the achievement, but I'm enjoying it and keep on playing. The creator has chosen to have the grind be brief (each level takes about 20 seconds; you either win or lose in that time). I think this is a good choice, as it lets the looting happen quicker. And that's the fun part: attack, loot, get stronger, repeat. Well done!