Thanks for playing and the feedback!
We are working on redoing the tutorial, and trying to figure out how to add bits of it later, while still fitting it into the story. One planned change is to add a popup based tutorial for the inventory and combat that will highlight each section with a brief description. We are also looking to add some dialog later reminding players of key info, such as giving items with matching affinities to each Slime to boost their effectiveness. The semi-random berry bushes will probably get an update mentioning who the berry is best for. The fight with the knight is much easier if your Slimes are properly equipped with matched affinity items. We did not do a good job of encouraging players to mess with the affinities up to that point, which makes the fight harder. That fight had also been the end of the content when we started adding story, so was meant to be a challenge. As we add more story we will reduce the difficulty of the fight a bit so it is not such a big jump.
We are doing the art ourselves for this game. We started with some public domain assets, and a recent update was swapping to our own art. We are still fairly new at pixel art, but are working to improve it. This game has a lot of items, requiring a lot of art, so getting everything replaced took a lot of time, and we did not get as much refining done as we wanted.
I'll take a look at the drag and drop. Were you dropping onto a slot, or just into empty space in the bag?