I'm not going to rate the episode on a one to ten scale, because I have a hard time even ranking it. Sections of it were by far the best out of any Discovery episode to date, sections of it fell flat, and it left me wondering about the series as a whole.
The good: Visually speaking, this episode was a feast from beginning to end. The opening combat scene was the best in the series to date - lasting longer than a few seconds, and giving me a semi-clear idea of what was going on. The planet was absolutely beautiful and had nice alien touches - far better than any away mission on any of the earlier TV series . The planet-side scenes had a very heavy TOS vibe, as others noted. The characterization was good, the dialogue was more natural, and the Klingon scenes were not totally boring.
The bad: As was mentioned upthread, there wasn't much of a plot to speak of here. The episode really relied to a great degree upon the very special special effects to hold our interest, because so little was really happening planetside. And the Klingon scenes continue to frustrate, because there's lots of things which look like plot development, but are left ambiguous enough that nothing ever gets nailed down (whether or not Cornwell is actually dead being the most notable example).
The series as a whole: I think, as episodes of Discovery go, this might end up being as smart and well executed as they come. But it still seems remarkably shallow to me. I mean in the sense that if you strip back the character development, the whiz-bang visuals, and the overall plot arc, I just don't really see any overriding theme here. Not every Trek episode needs to be a "message" episode, but I'm not sure we've seen a single one from Discovery yet, and I'm really mourning their absence.