Probably my favourite jdrama out there in terms of acting, scripting and originality. I agree with everyone else. If you're looking for some cute, happy fluff - you should turn away and look elsewhere. But if you're looking for a dark mystery/suspense with a touch of romance, you probably won't get anything better than SoraKara in this genre. The drama does start off kinda slow and a bit annoying, but the overall story is completely worth it.
TBH started this because of Kassy (the lead actor), and I think he did a pretty good job as Irie. I agree though it could get a bit annoying esp with Kotoko around, but if you went back to the original sources, you'll find that she's not exactly a peaceful character in the first place. So I justified the annoying-ness of this jdrama with that. This is the only version I was able to sit through without wanting to throwing something since it deviated from the original story, so it all comes down to personal taste I guess.