I'm not very good at animation, but let's see...
First, explosion animations rely very strongly on timing. The initial blast should be very fast, with it slowing down as it progresses, to eventually the smoke wisping away.
Secondly, you're not mirroring this but to be honest I could hardly tell the difference. That makes it seem like a lot of effort is being wasted. Try to make the shape of it all look less mirrored by giving more unique design to the explosion, or just go ahead and mirror it.
And lastly, it's hard to really see how this is ACTUALLY going to work without the smoke. Smoke is just as much part of the explosion as the fire itself, and ties it all together. Remember though, that the fire will somewhat burn
into smoke. You can also improve this heavily with some effects. Most explosion animations rely on a very quick flash of white before the explosion, adding a sense of intense power to it. You can also try adding a 'shockwave' of smoke under it like I did in mines, I feel it really adds a lot to the explosion.
References are going to help you a long way here:
http://pixeljoint.com/pixelart/36235.htm - not so great timing here, and a different perspective perhaps, but I think everything else is spot on.
http://pixeljoint.com/pixelart/47800.htm - minus the towering flames, this portrays a lot of what I had pointed out(still somewhat bad timing, so maybe I'm wrong about that!)
http://pixeljoint.com/pixelart/30769.htm
Also, there are great pixel art game references out there... I think Metal Slug is one of them. I dunno, I never played them types of games much. Make sure you take into consideration transparent smoke(not dithered, but alpha)!
edit: I also noticed you have a bit of pillowshading going on in there. Shade your shapes based on form and volumes, not by outlines! And I promise, last thing... the color of explosions will vary. Like the references above should show, they will mostly start off strong red/orange and intense and fade darker as they burn off into smoke.