I'm not going to claim to a great expert of Shounen or even Tournament Arcs in general, because that's not really my scene, but I'd be surprised if you still had the same feeling once the Dark Tournament Arc concludes.
People do like to go on about how it's one of, if not the best, Tournament Arcs ever and while I lack the genre knowledge to draw a plethora of comparisons with other works, I think the strengths of the arc are easily highlighted:
- Set-up: The central villain of the arc, and his strength vs. the strength of our protagonist is established even before the arc begins. This 'laying out the tracks' so far in advance makes the build-up, and eventual conflict with the Big Bad, more satisfying.
- Story Relevance: Related to the above, the actual reasons for our heroes to take part in the tournament is established for not only purely dramatic reasons, but for emotional ones too. Our protagonist has an extremely compelling emotional reason to take part in the proceedings and take out the Big Bad, and it's not just "save the Earth" or "Be The Strongest Fighter".
- See Our Heroes Do Cool stuff: Like any good action series, seeing characters pull off unexpected and cool powers that have only hitherto being hinted at is pretty exciting and fun. Surprises are cool, and when you have our characters get to strike out on their own they get to pull off some pretty interesting stuff.
- Akiyuki Shinbo: Shinbo was heavily involved with the direction and storyboarding of various episodes of YYH, but his best and most memorable work in the series is his work on the Dark Tournament Arc. Often, shounen is a genre where individually talented directors and animators get a chance to run wild every so often, and what better place to do than in a tournament arc where lots of crazy things can occur. Shinbo is a director whose highly striking subjective style makes him uniquely suited to depicting these kinds of events.
- Catharsis & Epilogue: Not only does the finale of the arc providing some very satisfying emotional pay-off, but it's also followed by an extremely powerful epilogue which I won't get into here. Suffice to say, there's significant fallout from the events of the arc which get paid off in a very memorable way.
- Cute Commentator Girls: Need I explain this point?
I mean, I guess on the downside, it is still pretty long. But in a way that feels more earned than normal.