Nice Howard, really nice.  I like the recoil-effect on the weapon;  the orange thing below screams laser-targeting system to me   Perhaps if you offset the barrel's recoil more - so it was bang / BANG - a few more frames between the two barrels firing / recoiling...

The fur is nice - I think that will stand out a lot better against your BG elements.  I think there should be some more hip rotation resulting in some up/down motion on the hips as he plants and pushes off w/ his feet - something to consider.  Perhaps some more specular highlighting  - it's a tad dark in your processing build linked above; hair at this scale is hard to duplicate though - and should be anistropic if shiny.....  hrm. 

What AA & rendering engine are you using for these?  Scanline?  I gotta say, the antennae thingies aren't my cup of tea, but they help convey the motion - I'm curious to see if they'll get lost with the cannon up on his shoulder or what.

KEEP IT COMING  

full of awesome as usual.  I'd love to see details on your workflow from max (ie, what anti-aliasing settings, bg color, alpha matte / processing if any, sprite-software steps, etc.,) to these apng's - extremely impressive.  I've been using 3dsmax since, well, since it was 3ds on dos and this stuff just slays me with awesomesauce.  HUZZAH.

On the gorilla:  Perhaps more movement in the hips & back - it looks too solid / inflexible.