Oh this is actually a pretty nice simple game! Let's go through the details:

The Good:

The tutorials, and learning the mechanics took a while but after getting used to the controls and the gameplay, it can become an interesting strategic and reactionary game in choosing the best attacks against the skeletons.

The art is well done in this game and the effects are also well placed, so it landing the super charged slam attack can become intuitive which is good for players.

The score system is a good touch for replayability which suits your core gameplay very well. Good choice on that design!

To Improve:

The supercharged attack seems very powerful because it is required to kill armored skeletons, and can hit in a large AoE making it the go-to attack 90% of the time. I think if you tune the skill's ability a bit, such as making it attack in a smaller AoE, it would be more balanced and engaging to play. This does mean you'd probably have to sit down and playtest a bit more because the it may be difficult to use the skill if it doesn't have a strong AoE as it takes a long time to charge.

But by making the supercharged attack have less AoE, there is more urgency to use the other attacks that take less time to charge, and create more dynamic gameplay.

But the biggest weakness is probably that the game systems each feel like they were designed in isolation, there is no core experience the game is designed around. The current game gives off a vibe of a last-stand kind of experience, so if you ever take this game further, I recommend you to design based on that feeling. Some of my suggestions would be, maybe have a giant immortal skeleton that spawns 10 seconds in that you cannot kill, but you can only knockback by using the ultra charged slam attack? This gives off the feeling of the inevitable end which is what your game is kind of centered around. If the giant immortal skeleton passes you, you instantly lose no matter how many lives you have left - so this gives it an immense threat, as well as a sense of dread, fear (but also courage).

Nevertheless, very nicely done!