Played Steve once, and he's not for me. But good for people who enjoy Minecraft or his moveset. He just feels so stiff to me and the tiny jump is a killer.
I think it's a fine addition. They seem like pretty unique characters with block building so I'm looking forward to finding out more on Saturday. In terms of importance as far as Smash announcements go, it's definitely up there with the likes of Snake, Sonic, Cloud, and Banjo-Kazooie.