I have played for about an hour and here are my first impressions of this game...
You start with 100 population in the beginning and everytime some enemies go through your defence, your pop goes down. So if you play bad for the first few level you are able to continue but at some point you are not able to do any mistakes because the game would end if population reaches 0.
There are 5 types of towers to place. A fast shooting machine gun for air and ground units, a mortar for aoe damage, some freezer to slow down enemies, one for air units and the 5th tower is like the first tower but it shoots faster and attacks only ground units. For killing units you get gold and after some time your towers receive enought exp by killing units so you can upgrade them a few times and they have a bigger range and shoot faster. There have to be some space between the placed towers, so you cant just spam many towers in a small area. Each tower also got a passive ability that has a special effect on each type of unit that activates randomly.
Each mission (i assume there are 10) can be played on 3 difficulties and you get either 1, 2 or 3 points for upgrading depending on the difficulty you chose. You can choose out of 40 things to use your upgrade points on. Things like earning more gold for kills or a lower re use of traps may help you to come back to precious played missions again to do them on a harder difficulty. Furthermore there is a minigame for each completed mission to get 1 upgrade point each. So it should be possible to unlock eall 40 things in the skill tree (10x3 points for missions + 10 for minigames)
That brings me to the next point: traps/skills.
When you progress in the game there are up to 5 special skills unlocked that have to reload after their use. They cost also some gold to use.
The graphics are pretty nice. Even though im not a big fan of super nice graphics because a good game counts more for me.
The sound of guns is pretty awesome too.
10 missions plus 10 mini games should still take some time to complete. On 2nd difficulty it is pretty challenging too and you do not get everytime 2 points (2 points for 2nd difficulty) when you let too many units walk into your base. So it may be smart to do every mission on easy and try again later with more skills unlocked.
Ok, there is no pause button ingame, so sometimes it gets a bit hectic especially when some enemy is close to your base and you have to think of what trap/skill or tower to use to stop it. But you can prevent that by not running the game on a high speed so you can look at it early enought.
So all in all it is a nice game of a small developer team and publisher. I would give it a 8.5/10 rating