You can see how the WiiWare version of Sonic 4 compares to its HD counterparts by checking out these new screenshots.
Nintendo's US website tells us that the WiiWare version will feature online leaderboards for anyone wishing to post their speed runs. However, it also says the game will feature 'Full HD resolution and wide-screen format.' Whooops.
Sonic 4 project lead Takashi Iizuka recently told ONM that all versions were pretty much identical. "Basically we prepared identical game content so users could enjoy playing with their preferred hardware platform. However, some hardware specific capabilities are implemented. For Wii, you can enjoy a special stage by using the Wii Remote's tilt control."