Hi!
Looking cool so far. 
I’m no explosion expert, and I have mostly the same feedback as Petrie. The ring is really sharp and attracts the eye, where the center of the explosion itself should be the focus. Also, its timing looks just a bit slightly off. I noticed that issue when I’ve been making explosions myself. If you make your explosion super bright for one or two frames then suddenly fade them out, they will appear to reduce their size.
Here, your frame 7 looks big, powerful and super bright. Then, the frame 8 shows your shapes but the core itself is greatly reduced. In an explosion, the core should always expand (unless it’s a very fancy explosion where everything is sucked in afterwards, but I don’t think that’s the goal here).
In the Overwatch gif you show, the initial shockwave is really fast, showing the AOE size of the explosion. Then, you have the actual shapes that appear and linger for a bit longer. Think of it this way:
- Initial burst, not longer than 1 frame (max 2). Tells the player that something is happening/about to happen at “this” point in space and immediately redirects their eyes.
- Full-size explosion, showing the AOE range, mostly thanks to the shockwave. Should only last a few frames too. I’d say maybe around 4-5. Sparks then reach their full size and the shockwave fades out with them.
- You perceive the debris of the explosion: smoke, fire, etc. Those elements develop and linger longer than the rest, and should not attract too much of the attention.
Here are a few good examples of explosions that show this very well in my opinion (especially the first one):
Hope it helps!