This sweater is meant to be a bit "Ironic". It is sometimes labeled "Terrible Winter Sweater". There are similar 8 bit & 16 bit themed official sweaters for other games popping up to wear in some sort of "tacky irony" way. The sweater itself is not overly busy, nor particularly tacky looking. If the design had been on a tee, it's likely no one would have batted an eye at it. The way the sweater is knit, helps the art to look 16 bit pixelated.
The Green Hill Zone ground has had white trees added to the background & the sky has various sizes of snowflakes & dots added. Giant Sonic stands in the foreground, while Eggman in his Egg o Matic is shown flying in the sky. The snowflakes continue on down the long sleeves. This is an adult sizes only item in fall/winter 2014. Where is it sold?