The original Mega Man was available on the Wii U prior to today, but evidently Capcom has decided to announce that Mega Man 2-4 are available on the Wii U eShop right now, with Mega Man 5 and the underrated Mega Man 6 on the way at a later date. As usual, the games are priced at the typical $4.99 price-point, and come with customized controls, Wii U GamePad support, save states, and their own Miiverse communities that are also up now.
If you're curious as to what Mega Man games to buy, I would go with 2 right off the bat, as it's the most beloved and iconic in the series. You can check out my opinions on all of the classic Mega Man games right here and decide for yourself though (hint, 3 is actually pretty great). It's a good day for Mega Man fans, even if Nintendo did most of the legwork.