Hey,
This game was very stable. and cute. I think the major issue with the game is the balancing of the game. Implementing more towers will definitly change how you'll want to balance the game later on, however you'll still need to do balancing. This Saturn tower is way too strong for the current wave system. At one level up and with some good placement you can get to level 23 without moving a muscle while astral gems just pile up. You reach this state within 3 waves, giving you have a solid 20 waves of gems to collect.
I think the waves are very well designed and really good for balancing a game. The waves have a good variety of tanky and slow, squishy and fast, and even in-between enemies.
The Saturn(1+) tower is overpowered for a variety of reasons. It has a very large radius which means that any enemy fast or slow will stay in its range for a very long time. It has multi-targeting which makes it really good against all enemies. Multi-target makes the amount of enemies irrelevent since they all take damage the same. Multi-target can only be countered by different enemy types. Typically really fast or really tanky enemies would be a counter for this, but the large range counters the fast and squishy enemy types. I would recommend cutting the tower's damage a lot and possibly not increasing the range, or only increasing it with another damage cut.
After some testing the the base tower looks pretty balanced
The general movement and feel of the games core mechanics were really good and spot on. I particularly loved the ice and the gem pickup/toss mechanic. I loved stacking up gems and then pointing in a desired location and spamming E.
A label when hoving over the storage, shop, or blackhole would improve first time understanding of the game.
This game is very nice and relaxing, I've enjoyed playing it and testing it quite a bit. I think the game will get more hectic with more towers and better balancing. I think a solo-target push back tower like a Jupiter tornado or the winds of Neptune (700mph average). Another tower could be single target projectile like the dart monkey in bts would really help in finding a good balance for things. I think the ability to craft the gems into a higher worth gem (yellow gems) can greatly help the gameplay. I do like how the towers are stationary during a wave, but I think a system that can induce more hecticness is to allow the player a certain amount of tower moves per wave.
Overall, very high potential game with a really solid grounding.