I shall put my two cents in, being an avid fan and collector of all things Sonic the Hedgehog the Archie Comic Book series, I decided to get some of these figures to have representations of the characters from the games/comics.
Tails is indeed quite a wonderful figure.
Sonic on the other hand... He requires hand support for any action poses, due to the size of the figure and the large head on such a small body/frame he suffers from top heavyness. If you want him to stand for any length of time, without ever touching the guy, you have to pose his legs in a perpetual spread open pose with the feet facing crookedly to the side rather than facing front.
If you try to alter his pose, you will fight with him to get him back to standing, but he is a highly poseable figure for such a small size. With all the same joints as Tails.
I too have held off on getting the Knuckles figure, oddly enough if they'd included a Super Sonic with the comic pack and priced it at 15$ cnd it probably would fly off the shelf. As it stands, who wants a transparent Sonic?
I too also wish they had a few chaos emeralds and power rings to interact with, or at least display with, but even the larger 6" figures don't have any of those, which begs the question, WHY? Every Sonic videogame features Power Rings and Chaos Emeralds, so why don't any of the dang nabbed toys come with the most basic accessories?
I hope they make an Amy Rose, a Rouge and a Shadow in this size range, with the price they have it would be simplicity to include those three, I would hope after all they are highly popular. Just as popular as Sonic, Tails and Knuckles.
And by the by, here's hoping that they include a couple of Badniks and good ol' Eggman for these guys to fight against.