A decent use of 5$.
Unlike Sonic 1 and 2 on the Sega Master System, Sonic Chaos copies the controls and gameplay from the Genesis Sonic titles almost perfectly. You are given the option to play as either Sonic or his sidekick Tails. The controls are as simple as ever. All you need is a D-Pad and a jump button.
Pressing down on the D-pad and pressing the jump button will make Sonic or Tails spin-dash. If you don't know, the spin dash has your character curl up into a ball and launch forward at top speed. Holding up on the D-pad and pressing the jump button as Sonic will have him use a move similar to the spin dash, but without the added protection of being curled in a ball. It's useless. Using the same button combination with Tails will make him fly into the air, giving him a major advantage over Sonic.
The levels are well designed. They're filled to the brim with springs, spikes, loops, and badniks. They're also very large. The large and elaborate stage design seems to come at the expense of the bosses. Bosses are incredibly simplistic and require very little effort to defeat. The Sonic series hasn't always been known for it's bosses but a bug robot that simply requires you to spin dash into it repeatedly without any resistance feels a bit too simplistic.
The graphics are colorful and each stage has it's own unique look. For an 8-bit game there's a surprising amount of detail in the stage and character sprites. The music however, is just bad. Apart from maybe one or two catchy tunes, there is nothing memorable about this game's soundtrack. This is a shame especially because most Sonic titles have excellent music. The rest of the sound is fine for an 8-bit game. It certainly can't match the quality of the genesis titles but it gets the job done.
Overall, it's a decent game that will only cost you five bucks. As far as platformers go, you could do better and you could do worse. It's definitley worth a look if you're a Sonic fan.