Hello!
Take a look in my game:

This is my first LD I’m very proud of my LD24 game! It looks great! I’m not an artist, so this is very good graphics for me.
I’m new to HTML5 too, but by this tiny contact than I’ve with it, it seems to be the platform of the future! Easy to learn, easy to use, supported in any operating system, no proprietary tools needed, and a very high level language to program.
My game for this LD was a simple player-evolution and action based side scrooler. What I’ve to say about making a game in 48 hour is:
1. Make all level design *first*: I’ve designed at the start only one level, and because of this, I had to design other in the last 15 minutes of the LD.
2. Art is after *all*: If you’re alone, don’t try to make the art first, or any bug in your program can make you to extrapolate the time.
3. Write you physics before the LD: Physics is cool, but only if you have time to deal with it! Otherwise the physics can appear broken in your game.
4. USE PAPER!: This is very important! The state-of-the-art tool to making game design is PAPER, or even better a WHITEBOARD!
5. Know your tools: The last four hours of the LD I spent trying to find a strange bug in my engine, and after all the bug is solved by a simple javascript array trick.
Well That’s all. Please play my game and have fun! (or not).

P.S: My game is 5 star, isn’t it? So, please rate it 5 star!
P.P.S: Sorry by my english :). I’m brazilian.