I will say that a long-running arc for television was kind of a new concept at the time**, but it was executed so poorly that it almost wasn't even worth it. It did set up Crockett and Tubbs leaving the force at the end of the series, but I feel like this could have been accomplished without Sonny losing his memory. I mean, over the course of four seasons, he'd gotten divorced, seen friends betray him, and watched his new, pregnant wife murdered right in front of him. And that's just the tip of the iceberg of shit that the character dealt with, so it would be understandable that his wife's death would have pushed him further over the edge. It was just unnecessary to fuck with him even more. It doesn't help that the resolution was so unbelievable that it nearly made me refuse to buy the last season on DVD (I did end up buying it because I'm a completionist).
What I would have rather happened would have required the series to end a la The Dark Knight Rises, where, sure, Sonny could have been involved with the boat explosion if they really wanted a dramatic finish, but then he sends Tubbs a message, letting him know he's alive and well on Cuba or something, now free of the burden of fighting crime. It's not a great alternative, but at least that way, we wouldn't have been forced to watch the crap bag that was Season Five.
Runner Up: Zito's death in Season Three actually hit me harder than I would like to admit. While Larry was definitely more comic relief than anything else, I felt like a lot was lost when he was forcibly overdosed on heroin. I know the character had been written out due to the ratings fall when Vice was scheduled opposite Dallas, and John Diehl wanted to focus on his movie career (which pretty much went nowhere, but alas, hindsight is 20/20); but that doesn't take away from the fact that Switek's continued existence on the show was essentially superfluous, enough so that they had to create scenarios by which to keep him moderately relevant. Sigh.
BACK TO CHALLENGE
* My mom used to watch The Young & The Restless every day, and during college, I became obsessed with Passions. As a matter of fact, I still miss the hell out of that show and think television could use some of that insanity nowadays.
** They tried earlier in the show with the on-again-off-again relationships between Sonny and Gina and Tubbs and Valerie, but they never attempted something of this scope.