Surprisingly enough, this is actually the first substantial cross-over between The Original Series and Next Generation (I’m not counting the 30 second cameo of Bones in the pilot).
Sarek is an interesting character, and the Vulcans have been very underused in Next Generation so far (in fact, according to the indispensable [Memory Alpha](http://memory-alpha.org/en/wiki/Vulcan) there are only ten Vulcan appearances prior to this one in Next Generation).
The episode doesn’t quite make it into ‘great’, and I think that’s mainly because it relies a lot on internal conflict and psychic communication, and that simply doesn’t work very well on screen.
178 down, 559 to go.