I'd say about 60% of season two is spent with the Grounders or in their camp. Octavia begins to learn the language and starts to bond with them, and they sort of team up. I don't want to give much away, but the Grounders are incredibly important in season two and you meet Indra, Lexa and a few others who become very important. Lincoln is a main character in season two, and there's basically a running theme of the Sky people fucking up a bunch of shit and then having to fix it. Clarke and Bellamy become the ring-leaders and Octavia and Lincoln become like the gap-bridgers, and Monty gets a bit more screentime (though not enough!) and Jasper becomes more of a pain in the butt. Also, Clarke holds her ground on Finn being a dick, which I love, and Raven definitely gets a good arc. I really think you should keep watching! :D