Grong VS Devil Part 1 Needs a lot of work
Clearly this is the work of an aspiring flash maker, so let's not be entirely derogatory.
This game could use polish in every area.
Level design:
There were issue in which objects that could not be seen were blocking the way. Jumping puzzles are meant to elicit skill on the part of the player, not showcase invisible walls from the start, generally you add these types of twists once the basics have been learned. Health gathering seems pretty unnecessary since once you pass the first enemy, it is incredibly difficult to actually make your character get hit by the enemies. I would recommend placing these in harder to reach locations or having fewer of them.
Mechanics: Not being able to jump while standing still makes no sense. Also, our hero apparently is wearing greased shoes. Fluidity in this regard is difficult to attain. In a platformer like this, you don't want too much slipping, but you also don't want your character to stop abruptly. This is a more difficult aspect that you will get once you watch a few of the classic successful platformers.
Sound Design: Picking up items, getting hit, maybe even jumping are usually associated with some sort of sonic influence. Try coding some sort of sound for these events, as the game feels empty without something acknowledging you actions (background music would be good too).
These are a couple of pointers. Keep trying at it and eventually you'll come up with a game that people enjoy. Don't be too discouraged by early failures, they're all a part of the process.