Game feels like a bad spinoff of Kingdom Rush. Needs a lot of balancing/polish/changes before it'll be anywhere close to that level of quality though. The grammar in the upgrades section needs a lot of work too.
The blue birds in area 5-1 and 4-3 are way too OP. especially in 5-1, they one shot your group, sometimes before you can even get one attack in. They're level 46, I'm level 49, and I still get wiped.