Thank you very much for playing, and for your detailed feedback!
We originally planned to list the descriptions with item icons, but in the end because of time constraints we ended up only explaining everything in text. Tutorials are not the highlights of game jams anyway. :D As for upgrades, each item gives a permanent boost to the character. Giving immediate effects (like when a med kit is picked up, the character becomes immune for a few secs) was something we only added last minute, and we didn't have time to add something to all of the items.
The AI is pretty simple, really. It always shoot the enemy closest to him, and if there is an item, it goes straight to it. Definitely a lot of improvement could be done on this front. ^^