I tried it. It was what I expected, a really good take on online shooters. I don't like online shooters, so it wasn't for me, but a great game of course. They should have some idea on how to compensate for lack of voice chat though.
From what I played. The main online mode is about covering ink, you see a spot with no ink or enemy ink? cover it. See that X? A team-mate died. More too. VC isn't that important in the main mode, though may see more use in the ranked battles.
But Splatoon does not need voice chat, the Wii U does. I won't ever use it probably, but they kinda had a idea with Wii U chat, and it never happened.