Great engine! Decent game.
Graphics: Sprite graphics with original characters are always cool, and these characters are very nicely done! Unfortunately, some of the transitions like the "get ready" text break the player's suspense of disbelief by mixing pixels freely with vector shapes. It's almost always better to go either all pixel or all vector.
Style: The strongest part of this game was certianly it's original style, theme, and characters. Nice work! Combat works well enough, but the way enemies and the player die could be embellished a little bit if you really want to nail that classic 2D platformer look & feel. Think "fall off the screen when you die."
Sound: The music gets the blood pumping, but it seems to clash a bit with the characters and the world. Sound effects are good. Though you probably ought to replace that one mario sound effect with something more original. There's tons of free sound repositories out there.
Violence: Jump on the brightly colored toasters to, well, break them, I guess. No biggie. Jack Thompson has bigger fish to fail to fry.
Interactivity: A competently executed run n' jump (by Flash's standards, anyway.) The controls could be further improved by not allowing a held-down spacebar to equal bunny-hopping. It would be nice to collide with the sides of a block instead of just the top of it, but I know this is hard to code. If I were you, I'd make it easier to land on a single block by upping the horizontal decelleration if you're on solid ground, and perhaps capping the maximum fall speed so the player has a bit more time to react. (Or by making all the relevant platforms more than one block wide.) Collecting butter is easy and I could not impove upon it. Good work, there. Combat is decent, but could be further refined.
Humor: The cocnept of anthropomorphic toast is kinda goofy, but it would be even better if you'd add some sort of story with dialogue or even voice samples. Flash gives you an amazingly broad range of tools with whiche to tell a story. It's a shame not to use them. If you absolutely must stick to the pixels, at least add a little intro screen where a big evil toaster steals the bagel pricess or whatever. It would enchance the characters, which are already this game's strong suit, if you add a story to them in a way that engages the player.
Overall: You've done an excellent job of programming this game's engine, and a great job designing sprite characters. The control/gameplay could use a little tweaking, but the real missed opprotunity here is one of storytelling. I'm sure this game will score well, and it deserves to! But if you take it a step further, and really refine it, you could have one of the top 10 truly memorable Flash games of all time here, or a damn fine proof-of-concept for a GBA game. As it sits, you just have a competently executed flash platformer. If that's all you set out to accomplish, good job! :) But keep working on it and in another month or so, it could be SO much more!