I think it's fine for the demo now that I know the last one is sandlands-4. I think the difficulty curve is too steep (for me) if there is more game. I would be frustrated for not getting past this point. (I still haven't managed to beat sandlands-4.)
I'm definitely going to reduce the difficulty at least a bit. I'm probably going to start rounding up some playtesters soon. If you'd be interested in playing more of the game early to help with game balancing and minor bug hunting, join the Discord server linked in the game page (that's where i'll be hosting playtesting). If you'd rather just wait for the game to be done and good, then that's fine as well :)