I give it an B+.
It has certain similarities with TOS: The Paradise Syndrome, and I wish The Inner Light would have taken its approach to integrate Picard into Kataan society. In other words, I think Picard's memory should have been entirely erased at the outset. Rather than coming out of a fever, he should have just assumed the role of Kamin, say during his wedding ceremony, ending the teaser with Kamin/Picard saying "I do." I'd have had Kamin dream of a starship over the years, musing to Eline how real the dreams seemed to him, in anticipation of the illusion collapsing altogether when he watches the probe launch.
As it was, "When do I get you back?" was cringeworthy dialog, as was "I'd like to ask your permission to build something. ... A nursery." My suspension of disbelief was severely strained. Picard would ever give in to the illusion, if he had any actual memory of the Enterprise, much less one that was as real as his present life experiences. The conflict over pulling him into the illusion was artificial, unnecessary, and for the story to work as scripted, Picard had to act against his character as captain of the Enterprise. Wank all you want, but this episode needed some rewrites with respect to this issue, which is why I can't give it an A.
The basic idea of a high-tech message in a bottle, which is all that's left of a dead civilization, is fabulous though.