Besides the amazing first episode, and the interesting ideas in the last one (plus the very end), absolutely nothing in between did anything to add depth to the characters or make the plot more interesting. In fact, it just amped up the worst parts of this series (as explained below).
But here's a controversial opinion: the Endless Eight was not the worst part of the series. Hold your gasps. Really, it kind of baffles me how nobody is complaining as much about "the Sigh of Haruhi Suzumiya". I mean, it feels and acts exactly like Endless Eight — it's an arc that should have been way shorter, it gets progressively more aggravating to watch, and it seems like a joke. HOWEVER, in the very LEAST the Endless Eight was ABOUT SOMETHING.
I'm not going to defend how boring Endless Eight was, but you have to admit it was an ambitious idea. And you could see what they were going for; having to trudge through the same sequence over and over put you in Nagato's shoes. It was simply an interesting premise, executed like a disaster.
What did you really get out of the Sigh of Haruhi Suzumiya? That instead of being a flawed character, our protagonist is really just an asshole who gets away with everything? That Kyon is ridiculously overdramatic? How did we benefit from that arc? Through the 4 episodes, every character became more of a caricature than the role they played in Haruhi's film, while they series itself repeatedly bashed us over the head with rules and concepts we already knew. With exceptions to the almost philosophical theories part V presented, nothing in the arc was helpful, or significant, or fun to watch.
The animation was great though.
