I highly recommend you play this game. It’s one of the first games I ever played and I know from experience that it’s one of the best Sonic games in recent times.
Sonic colours is full of levels where your objective is to reach the goal as fast as you can while collecting gold rings in order to get a high ranking. There are also a few levels where you have to get past obstacles by, for example, hitting switches to make things move. (If that sounds boring to you, congratulations, because they are. But there’s only a few levels like that in the whole game.)
New to this game (I would say exclusive, but that would be a lie) is a race of beings called wisps, who grants Sonic certain abilities that he can use to get through the levels. The White Wisps are the most common, and allow Sonic to fill up the Boost Gauge, which is used to go faster than he can normally.
Then there are wisps that transforms Sonic into different forms. The Yellow Wisp, for example, allows Sonic to use the Yellow Drill form. It is used to travel through the ground, which is often where secrets are hidden away.
Speaking of secrets, besides the golden rings, there are also special collectables called Red Star Rings. There are five of them in each level, and they are pretty well hidden, so good luck finding them. If you do manage to find enough of them, they’ll unlock special levels in an area called Game Land. Seven Colours, three levels per colour, and beating every level in one colour grants you something called a Chaos Emerald.
Collect all Seven Chaos Emeralds and you can unlock Super Sonic. A powered up form of Sonic that has an Infinite Boost gauge, with the tradeoff being that using him drains rings. So you’ll need to constantly collect them to stay transformed. Using Super Sonic also doesn’t let Sonic use wisps, so be warned.
That is all. Once again, I recommend playing this, because it is what got me into the Sonic Franchise. Sonic Unleashed helped lead the way, but Sonic Colours is what really roped me in. Hope you enjoy what you play!