Woah...
That was the best best first timer I've ever seen. I have just a few tips.
1. Try to make Spawn's dialouge more badass and the Hulk's dialouge more, well, Hulkish. Like, instead of "Crap, time for me to use my new toy," it should be "Grrr. Hulk need to use new toy..."
2. If you can, try to find some sprites of Spawn with his chains, cause he uses them more than his necroplasm.
3. Voices would be great, but only voice it if you think that it realy sounds good. There's no better way for your flash to get blammed than to have bad voice acting.
4. Ignore the people who DO blam it. You can't learn to fight without busting a couple knuckles, you can't make a fame-flash without getting blammed on the way.