how is web browser not completely running away with the vote is beyond me. It may be tougher to implement than some of the other choices, but I took this poll more as a wish list than vote for which you want the most whilst bearing in mind which is the most plausible.
Messaging somebody online with "Hey wanna check out my new game, *link to game playable in browser*" how could anybody not find that completely awesome. In this modern age, less and less people are likely to download and install a lesser known indie game.
1. There's no way to make it compliant for every browser.
2. Probably no hardware acceleration.
3. Multi-player is impractical.
4. Not everybody wants to make "casual" games. In other words you cant just message somebody online with "Hey wanna check out my new game, *link to game playable in browser*", btw that will be fitty bucks.
5. Java, need I say more?