This is a good start, and based on the other comments I've seen and the fact that this is your first game, it seems that you recognize this is just a start.
Theme: not really any discovery yet. Looks like based on the description you were planning to put some treasure and secrets in, but it seems you didn't get to that yet.
Fun: I enjoyed it, but it did get to feel a bit monotonous since all there was to do was avoid the spikes and kill the enemies that were all the same. I'm sure with things a little more fleshed out (adding things like treasure, secrets, variety of enemies (including variety of attacks), variety of terrain) it would be really fun. Also maybe implement whatever that blue bar was supposed to track?
Controls: movement, aiming, and shooting all felt very smooth. However, there is one part that's very broken (not sure if I'd categorize this as fun or as controls). My attack range is greater than the enemies' radius of vision. That means I can kill the enemies before they ever notice me. I can even do this with the final boss!
Graphics: beautiful! I especially like the glow of the torches and the animations (the character movement is delightful, which is great since the character moves a lot).
Audio: I love the music! I love orchestral music, and it's fun to have a change of pace from the typical chiptunes that usually go with pixel art. The music also makes me feel like a proper hero, which is always good for a game like this. I did notice an issue, though: the music doesn't loop. This should be pretty easy to fix (just change the looping property on your audio player). Also, sound effects would really make the game feel more complete and immersive.
Originality: there's not really anything original about this game as it is, but that's totally understandable for a first game.