Not particularly complex (nor well thought out).
A very simple kind of defence-game, where the onus is on the player to take action towards leaving rather than "defending" (as the genre might suggest) until the situation changes. While an interesting and unique take on survival games, the fact there were pauses between waves allowed so much time to repair the balloon the game could be passed on the first day. Furthermore, because this was the ultimate goal of the game (with killing monsters as a secondary objective to pass the time) there was no need to engage in any fighting at all aside from the first few waves. A player could simply build a fort and sleep there until the threat passed, when he or she could then proceed to repair the balloon.
The stamina bar was an interesting addition. I liked how it affected accuracy if left for too long, but I felt there was more than ample time to sleep and repair the balloon between waves. Removing the pause between enemy attacks would put more pressure on the player to use their seconds wisely, and forgo making money for the sake of restoring accuracy.
I think the cost of traps was mixed up: single-use mines costed more than their permanent counterparts. There seemed no point in buying them when the money could be spent upgrading weapons or turrets to much more perenial effect.
It was also a little hard to get into- while the controls were seemingly straightforward, what to do with them was not. Jumping didn't seem to have much of a benefit, except to escape a few points of damage at best. Forts didn't seem to be damageable, so spending thousands of dollars on repair tools didn't seem like a very good use of the money. Furthermore, I didn't use my fort at all the second time I played through (except to house my turrets)- I could hold the entire army off with the machinegun, and healing myself on those rare occasions where I got hurt. Not being able to shoot from the top of a tower, despite having a clear view of the enemy and a loaded gun was also slightly frustrating. I think a better system would have been the enemies damage the tower if they reach it, forcing the player to occasionally make trips to the ground to repair it before it collapsed and needed to be rebuilt. It would also help if one could shoot from the vantage point they spent hours building.
The story, while not particularly deep or sensical, was quaint and not too serious. Good for casually picking up and playing.
The in-game achievements also seemed easy to get. I think more acknowledgement should have been paid to maxing out all the weapons or turrets or using all the traps. These things were superfluous to the achievements, which was a shame. It would also have been good to see some newgrounds medals coinciding.
Two bugs I'd like to point out. Somewhere along the sixth day (and 25th wave) it stopped showing when the next waves would be coming until several hours later. Despite an empty time-bar, supplies and enemies still came at regular intervals.
Secondly, the music of game-over overlapped with the music from the starting screen.
Although somewhat harsh, this review is not without praise. Though simplistic, there was something undeniably satisfying about buying the machinegun and mowing down waves of enemies. It is this addiction (and the drive to max out everything) that kept me playing for somewhere near an hour. Unless you're particularly motivated to upgrade everything, the game can be passed in five minutes or so. Nevertheless, addictive and enjoyable, but probably not worth playing a third time through.
~VelvetDarkRocks~