Hi, i don't know much about this game but the single player looks awesome + 4 player co-op seems like a great idea. But I'm wondering how will the online be? I'm mostly curious about rankings.

Welcome to the forum.

You mean ranks, or rankings? There's online leaderboards and extensive stat-tracking, but as to experience related ranks, no-one really knows yet.

For further information, check the FAQ thread, here.

In future, please ask questions in either the Ask the Devs thread or for direct answers from the community in the Ask A Question thread. Thanks.