Hello, and thank you for your feedback! Yes, the game is challenging, but we've playtested and adjusted the difficulty to make it more manageable but checkpoints would've been a good thing, we have a saving system but just for resuming the game if you exit, so in hindsight we could've implemented it and it would've been a good addition . Regarding the health issue, the game heals a percentage of your health at the start of each wave, so even if the health bar doesn't visibly change, you are definitely gaining health, it's more of a UI issue with the health bar not reflecting it accurately.
As for the weapons, you're right they may not be very detailed due to the 64x64 resolution constraint. We aimed to keep the screen uncluttered, so we had to compromise on the detail. We appreciate your feedback and will take it into consideration for future games. Thanks again!