The level generation feels just right for levels 1 and 2. The ratio of enemies to obstacles made me think about my turns. Not sure if it is just that I am bad at diagonals, but I got stuck at late level 3. Sometimes I anticipated that the enemy wouldn't push me because I scrapped another but I'd get pushed anyways.
The gems are a treat that I have to work towards and not just another piece that spawns on the map. Sometimes they're in a dangerous area, and I get one of those cheap thrills when I fly by to pick one up. The range of movement offered and their upgrade paths kept me engaged in that "one more run" feeling. The sound effects bring a nice pop to the game too. Love the shooting into space animation!