Wow, thanks for all the feedback, guys! I'm looking at #3 right now, with less lighting on the smoke, with perhaps a bit lighter and more transparent smoke towards the end of the animation.
In the meantime, I've made the death animation for the bumblebot. The idea here is that it's hit in mid-air, and spins into the ground and explodes. It will have a separate smoke and debris trail for added awesome.

I've also re-touched the weapon fire to better match the other effects...it's subtle, but necessary.

And I've finished the next enemy - the RollyPollyBot...I'm not 100% happy with the attack animation - I think it needs some work, but I'd still love any feedback you guys have!


I'll keep the vote on the explosion going for a couple more days - I'm in no rush to make a decision on this, because it's been such a pain so far to get something everyone likes.
Thoughts?