100MB is too big for a for a web app/game.
Even if you manage to put a 8-10MB demo, or a "first area", you'll still have to consider sharing the other 90% of the game to a number of user, and that'll cost ya bandwidth traffic.
But even if you can deal with that, it would be wiser to keep file sizes around the 30MB mark.
It all boils down to keeping the user interested - if you show them nice screenshots or a trailer demonstrating how cool your game is, it is more likely they'll be willing to download your game.