The Metal Sonic DLC is not just a new driver, but it also has a new track to play in Sonic and All-Stars Racing Transformed. Since the game feels balanced, Metal Sonic isn't any better or worse stats wise than any other driver. He has the same stat points as every other driver. You'll see him in races against you if you don't play as him. That could have been disastrous if he wasn't able to race against you. As a character, its up to you take him or leave him, but for me, this DLC is all about Outrun.
Once upon a time Outrun was the premier driving game. It seems only fitting that it gets put into a racing game. As a level it is half road, half water that will have you jumping over yachts via ramps. It is a beautiful, bright map with clear blue water. The course stands out from the rest and would really feel at home in the Outrun games. The course is pretty simple. Just a giant oval with no real twists or turns. The water part has different paths, but for the most part its free flowing and open. The road itself is pretty flat, but at least there are cars traveling down the road and plenty of boosters.
Plus you get about 10 - 20 new stickers that are just a bunch of expression faces. Not the same face, but different detailed round faces. The $3 wouldn't be worth it for the emoticons, its just a nice gesture to have them in here.
It is a nice value for $3 even if Metal Sonic relies on your personal preference and the course is simple.