Hey, this is a great arcade game you got here! The concept of being stuck within this circle and jumping to make triangles is a unique and well-executed concept, the overall construction of the game feels very charming, polished and professional, and the game has lots of variety and build-up with all sorts of enemy types that force you to play in new ways. There's also lots of nice little touches, like the triangles you build leaving paint on the background which slowly builds up. Great, classic, addictive arcadey high-score fun all-around!
If I were to have any feedback, it might be that I'd love if the scoring system was a bit deeper and allowed for more player expression and mastery. For example, being able to catch enemies in your triangles to kill them for bonus points, getting a style bonus if you 'graze' enemies as you build, getting a time bonus if you build your triangle quickly instead of waiting around, and so on! Being able to flex like this could add a lot of satisfaction and depth to the gameplay, introduce some exciting risk/reward as being stylish gets you closer to getting new lives but could get you killed, and most importantly, it would make starting new runs from scratch (which can be a bit boring due to getting used to the higher difficulty you were previously at) less repetitive.
By the way, you wouldn't happened to have played Resonance of Fate, would you? The whole triangulation mechanic? Oh, never mind...