Decent but not outstanding. I'd suggest reaching out to the Newgrounds community for Voice Actors who can REALLY pull off some really solid impressions of each of the featured characters. Also your sound mixing can use some more work, especially in the context of background ambience. It was rather odd to hear the sound of rain cut out between shots. Check out the site Freesound for everything you could need for your sound mixing.

The voice acting come on man it could be just a bit better. The animation was fair but i don't think you noticed that one of your characters lips doesn't move at all even though his mouth is covered. The worst part to me which is why it gets 2 stars is the title. This is suppose to be Batman vs Godzilla right yet no fight was shown or anything to show how Batman tame Godzilla. Just him ridding on his head and then eating joker. To many holes in the plot even if it is a parody.

Animation is excellent. Very smooth and fluent. Love it.
Voice acting is decent, no comment on it.
The introduction is a bit empty, could do for some rain sound effects in the background because I'm sorry to say, the rain animation is pretty horrible.
Effects in general such as lightning are wonderfully done.
Keep up the good work!

Okay. Godzilla eating Joker. :) You've got my approval

LOOKS AWESOME
STORY IS AWESOME
IS AWESOME