As I said before, we've seen will they/won't they so much now, it's hard to imagine a time where it was actually the first. Now, it's derivative and typically looked at as lazy writing.
Having the show so fresh in my mind, the actors were terrific, but I could really only stand Sam&Diane plots when it was part of the show and not the out and in front plot. I'm not really a shipper by nature, so inherently I'm not really going to be too invested.
I think a fundamental flaw is that this kind of plot isn't sustainable - it has to have some ending at some point. Sure, you can throw in some roadblocks like Frasier or the councilwoman, but you can't do that for 200 episodes. Regardless if Long had been difficult to work with, they ran out of what to do with Diane. Clearly, Long liked Diane enough to return to play her several times and also on Frasier, so it's not like she's sour. She was even in the 200th episode special.
Being the first go around, TPTB may not have really forseen it. And Danson and Long were so great that they probably wanted to ride it as long as they could. Even then, they got over 100 episodes out of it and were talented enough to retool the show for another 175.
I wonder in today's tv climate how a show like this could work. I think a little more drama into it than just comedy could be an interesting angle. Not that it has to be all 'gritty', but not all setup/punchline all the time.