A simple little game, and I enjoyed it. Curious to see where this goes and how it evolves. Do you plan to keep it an arena style combat game? Or is this just a sample of combat in an actual RPG/Adventure game you have planned? I see this being a really fun RPG game... fighting goblins and bandits in a forest... etc. Here's my feedback:
Overall Fun: I did enjoy it. 4 different enemies with their own strategy to defeat and attacks connected. Nothing felt off. I do wish it would have been a bit more challenging, though. I actually beat it my first go and only got hit once. The attacks are a bit delayed and slow for the enemies. It took me a bit to figure out how to hit the knight, but once I did... I could just circle around, hit from the side, and defeat him pretty easily. Also... I think the mage's fireballs could move faster.. or maybe they shoot a spread shot? Or homing fireballs? Something a bit more challenging to dodge. Despite that... I did have a great time with your game. Wish it was longer.
Art/Graphics: I love the pixel art and sky with clouds background. It's simple, but each enemy has a nice, unique look... and the artwork is done well.
Controls/UI: So... controls are simple and easy to understand. Move. Attack. I will say I'm not a fan of moving with arrow keys and attacking with space bar. Control options would be nice... maybe WASD to move and mouse to attack? Controller support eventually? Though... I know this is a prototype but if you do plan to do more with this... a couple keyboard options would be nice. Also... more special moves (charge attack, a lunge, sprint, maybe a dodge/roll eventually).
Sound/Music: The music was fitting and upbeat for battle. Didn't feel repetitive or annoying like some music. The sound effects were spot on! From the sword swipes, taking hits, enemy deaths, and I LOVE the scream as they fall off the ledge lol