Mega Collection has a lot of classic Sonic games in it, but some drawbacks in it as well. But still, a great collection.
It includes:
Sonic The Hedgehog: Genesis (1991)
Sonic the Hedgehog 2: Genesis (1992)
Sonic Pinball!: Genesis (1993)
Dr. Robotnik's Mean Bean Machine: Genesis (1993)
Sonic the Hedgehog 3: Genesis (1994)
Sonic & Knuckles: Sega 32X (1994)
Sonic 3D Blast: Genesis (1996)
Although, I wouldn't really consider Mean Bean Machine a true Sonic game, because it's just a puzzle game with Dr. Robotnik and some characters from the cartoon in it. Then, there are some other games from the Sega Genesis in it as well, such as Flickie. In my mind, I only consider it a true Sonic game if you can play as Sonic in it, but in Flickie, and Mean Bean Machine, you can't.
And 3D Blast was a total letdown because of its slippery controls, and the fact that it's just a crappy overhead view of an already bad 2D game. Don't play 3D Blast on this game.
But though, the games in this collection are great and can provide hours of fun gameplay into it, if you either are a Sonic the Hedgehog fan, or love the Sega Genesis. Either way, it's still very fun. If you have this for your GameCube and are thinking of getting some Wii Virtual Console games, do not get the ones in SMC, it'll be a waste if you already play one so much, and get it again.
They later released Sonic Mega Collection: Plus or the PS2 and Xbox that includes some Sega GameGear games from the sonic series as well, like the original Sonic the Hedgehog form Genesis, and Sonic Labyrinth (Which sucks ass. Don't play that if you have it, DESTROY IT!)
But it does leave out some pretty great other Sonic games like Sonic CD, Sonic Adventure, and maybe even Sonic the Fighters. But overall, this is a great game for any fan of Sonic, Genesis fanatic, or for collectors.