Ehhhh interesting but...
I know that this is repetitive, but your 'superhero slayers' remind me of Organization XIII from Kingdom Hearts, and even your story-line reminds me of similar plots. However despite the cliche and cheesiness of the dialogue and story, I do not think that it defeats or makes you series any less interesting. Besides with a series such as yours I'd like to see how many other classic concepts you can integrate into your series - I think this makes your series original in its own right; in other words keep on doing what your doing...its not too epic but its not a comedy, just the right mood for another great superhero series!
Now to other things, in terms of technicalities your sound effects were ok, flash animation was great, but there's still room for improvement, I think it could be more detailed. Music choice was meh, but it was alright. In terms of characters, for the superheroes try and stick true to the original characters as portrayed in the comics and the such; if the superheroes were to act way out of character I think it would really ruin the series. The dialogue and story-line, I failed to take it really seriously, they sounded so over-dramatic - but that isn't necessarily a bad thing :)
Just improve some of the minor details and this should be an even better joyride :) Of course this is just my opinion, your series is great already but it has the potential to be much better! It's got me hooked, looking forward to the next episode and more superhero smashin' fun :D