First, thank you for your interest in my proposal. I am sorry if some opinions below may seem a bit harsh, but they are my honest thoughts.

1. I understand that this is a prototype, but still a few words of description on the game page would help greatly. You can also use this to give simple instructions. For example, I have spent few minutes clicking on the every part of game screen, switched browsers and even started looking at dev console before it dawned on me that player is supposed to drag items to use them.
2. Similarly, you can add a screenshot and describe the meaning of various numbers and elements. This way you can avoid spending time on making tutorial while still giving some hope for the new players.
3. After some investigation, I think that numbers on item cards are: red- damage, green-health, orange-attack speed, blue -- I was unable to deduce. Also, it seems that some items have some kind of special abilities -- it would be good if they would be explained too. Again, for a prototype just listing them on game page will suffice.
4. It seems that the goal of the game is to maximize three values: damage dealt, combat score and time survived. However, current values for damage and time are not displayed during the game and it is unclear what combat score is and how to increase it.
5. The game is not quite turn-based :) That is not a problem, your game is actually is quite close to the genre I was aiming for in this topic. Still, maybe adding a 'pause' button would be a good idea, to give player better opportunity to think, especially if you do plan to add in-game descriptions for items?
6. Items with health bars feel slightly strange, maybe switch to monsters/pets/units instead? This, of course, is just my impression, there is nothing wrong with items too.
7. It feels that the game run takes too long now. Maybe start with less health and give player opportunities to increase health either during the run or as meta-progression?
8. The core concept of the game has potential, but it seems to be lacking an important element: the progression inside the run. Basically, what player sees and does at minute 1 is not in any way different from minute 5. Some (preferably diverse) ways to increase both player and enemy power would make game more interesting and replayable.
9. It seems that it is too early in the development to speak about balance. I am happy to look at your game again at a later date to explore the balance.