What's going on here?
Apparently Jazwares has decided to re-sculpt their 5 inch size modern Sonic. He looks good here, but how BEST to tell him apart in stores? His hands. If his fingers are fused, he is the OLD version.
His box does not announce the new sculpt, so you'll have to look him over. The hands will be larger than before, and the easiest thing to do is inspect them. They have a new joint construction (seen above right). The face is set up to be slightly different as well. (face compare photos pending) Figure may have head construction flaws, inspect all figures before buying! Photo by Lalam, turn-arounds & close up by Taaron
Photo by Taaron
Photo by Lalam
Photo by Taaron
These photos illustrate how the re-sculpt 20th Anniversary Modern Sonic compares to the old version of him (5 inch) & their Super Sonic. As mentioned above, you can tell him apart in stores by his hands. If the fingers are fused & 1 hand is closed, he is OLD (left) if they're both spread he is NEW (right) The other differences you can spot here are: new has wider shoes, different elbows, knees & no 'joint peg dots'. His head is also HOLLOW so he can stand better. Note the different head construction too (no ear seam) Over all the re-sculpt is a good buy. A figure that stands better, with improved joints & an improved face. The face on this one is computer sculpted so it's more accurate to the games.
Why not compare all the Sonics! With this new sculpt here, it may be the best/most accurate Sonic face yet. To prove it, here he goes with various other versions.
From top left you can see: Toy Island Figures Emeralds, Toy Island Sonic X Megabot 'fists hands Sonic', JoyRide Big Bendy, Toy Island 6 inch line SA, JW previous 5 inch line sculpt & last is ReSaurus regular. 
Photo by SonicToast
Photo by SonicToast
This photo has full body shots for everyone so you can see the sizes. Compared to this one, poor big 6 in Sonic is super goofy/off-model.
As a part of their winter 2012 box makeover, JW re-releases 5 inch regular Sonic, now without the "thru time" or "modern" labeling. The texture of the plastic for his head seems more matte, or different from the previous release. Did they resculpt him, or just choose a different material for the head? All other repackages have been identical, except for the box styling.
Photo by PacmanSonic138
The Super Sonic modern hand vs the normal, for figures of the same size. SS hand is less well defined/more 'blobby'.
You have made it this far down the page. Here is a picture of a Sonic figure that has no mouth at all. Isn't he strange?