Very difficult, many bugs, but fun.
It's a really good game, but it's just likable to me.
The worst part of this game is the defender enemies. They're too tough. As enemies themselves get stronger and stronger, the defenders (as they first appear) are freaking bulldozers. The wave before, you kill everything before it passes the first floor, then when defenders come, they make it all the way to your queen and you waste all your money setting up cheap defenses to stop 'em. The learning curve is too steep, and the enemy difficulty increases so fast, that one wave you're whacking off and the next you're spending money left and right, struggling to live.
The "corpes" (sic) pretty much makes the game easy as pie, or it will ruin you. It pays itself off very quickly, but the cost is a double-edged sword. If you can place just one and survive the next two waves, you'd have enough to place more, which essentially obliterates the need for any money afterward.
Plants > all. They fire from a far distance, and projectiles keep going. Not only that, but their upgraded forms just double and then multiplies their damaging power.
Slimes are okay, but you can't upgrade them while enemies are walking on 'em. Lame.
Skeletons, as far as I'm concerned, are useless without help. The runners fly by them, their hit range and attack are too poor, and their power is pitiful. Plus, they take forever to level up. However, once they upgrade... they're incredibly overpowered. At the last upgrade, they attack everything in range at once... really overpowered. lol
Bee nests are the third best thing in the game. They take a while to level up, and are a bit costly... but they pay off in large numbers. The fully upgraded ones have a huge range.
I really had no interest in anything else, or the diversity was too great among the other stuff. Dragons, mudmen, and demons just don't appeal to me.
I use this with every level, seems to work every time. First two plots, place a slime, and a skeleton, and then two plants further down on the first level. After the first wave, place a bee tree or two directly above the slime on the 2nd level. This works with almost every level.
Upgrade the skeleton attack to at least 10, and plant attack to double. Place plants on higher levels as buffers for any that may have escaped through the primary defense. If none get through and you can stock up 200 bones, start placing "corpes" at the top or upper 3rd level. Just place one, make sure you survive the next couple waves, upgrading attack and such when needed, then place another.
You only need 2 "corpes" to rake in the bones, placing any more is purely for the greedy. Instead of getting just 10 bones, I get at least 16, even more for tougher enemies. With the huge bone flow, I upgrade primary defenses of my plants, skeleton, slime slow, and bee trees... by then, only a handful of enemies get by, and I spam every open space on the 3rd and 4th floor with plants, which in turn spam-shoot anything that gets to them. It really lags the game down, but whatever.