Here's a size comparison shot for these 3.75 inch figures. Here, he's compared with the JW 5 inch regular Sonic and the old Super Poser Sonic. Don't write these off due to small size, they're VERY articulated!
You can see he's articulated at the knees, hips, elbows, shoulders and waist. The ankles, wrists and head are all turn-able. All figures on the line should have the same approximate articulation as Sonic himself.

"Plain" 3.75 inch Sonic looks great here. See all the different poses dispite the small size! Just like their larger figure, his head sculpt is quite well done and the eyes are well painted.

This figure does not suffer from 'werehog legs' as you'll notice his versatile poses. The figure is quite proportional and very Sonic-Like. Right photo by Jazwares, others by MichaelB218

With these close ups, you can see they still got his smile on, and that the figures shoe-bottoms are textured. All of the figures have near identical shoe bottoms, with number/maker and tread texture. You can also see the green paint for his eye didn't quite go on where the texture was stamped, but it still looks good and the face is very Sonic Like.

Not satisfied with Sonics' fist-hands? He can be modified.
*NOTE- any attempt at modifying a figure has the chance to break it.
This Sonic has Tails' hands from the same line. If you can get a Tails who has the colorless glove-band, you can switch their hands, and it will still look like Sonic hands (as the figures were not to scale) The hands are likely somewhat like a bead on the end of the arm since his wrists can rotate, so if you can get them off both figures without breaking the arm or glove, they can be swapped out, either one hand, or both. 

In 2011, Jazwares changed the card style for their Single Card Sonic 3.5 line figures. You can see that it's been simplified from the previous package. Instead of having the separate title-tag in the bottom, and raised shaped bubble, these all have a more square and simple bubble. The card top is angled, and has the logo instead. The card, as a whole, is also smaller. It still has all the relevant information, but is likely easier to produce and shelve. This is an interesting development for the line. Will it cause the 'older box style' figures to rise in collect-ability? (The 'black card werehog' sure did) 

You may be able to find the 3.5 inch figures at K Mart in the USA in spring 2011. When you see them though, they'll be in this newer more simplistic package. The Shadow may also be a darker color of black than previous releases. (side-by-side photo pending) If there's no TRU near you, give the K a try! Photo discovered by A Cat.

Photo discovered by Berzerker

 Discovered by A Cat