I'd give it like an 8.5. The acting and relationships were shockingly well presented, and it was, as promised, every bit as melancholy as Lost in Translation. So much of the film was so good. But there were a couple of moments that pulled me right out of it, mostly based around the futuristic tech. I know it's been compared to Eternal Sunshine, and I can see the comparisons and agree with them, but part of what made Eternal Sunshine so good is that the technology involved, while fictional, was handled in a subtle enough way that it didn't break immersion. Not as much with Her.
I was told it was considered a comedy. It had a couple of moments of humor, but I would never call it a comedy.