I've seen a lot of people complaining about this game's difficulty, but I think they're just looking at it wrong. You aren't going to win every game you play, but the fun is in the challenge of working out how to do the best you can with what you get, like solitaire. Plus, once you get a better grasp on how different enemies work and how to best conserve your health, you'll find that you win more and more frequently, eventually being able to achieve a perfect score with a little luck. So I don't think this game needs an easy mode, but I guess it could potentially use some kind of starting guide or tutorial. A little advice about the basic concepts and principles of play could make things a bit less counter-intuitive, and make it a lot easier to actually start playing the game. Once people crack through that shell, they'll find that it's super addictive and a lot of fun.
EDIT: I should also mention that, while I think a bit of basic gameplay guidance would be helpful for new players, adding a full description of all the monsters and how they work would be a bad idea. Figuring out little tricks and idiosyncrasies through play is, I think, part of the fun of this game.