Thinking of it in "hindsight", I really like how Kukui is the first legitimately difficult final battle in Pokemon.
While I think Cynthia is more difficult, Kukui actually tries to strategize.
Instead of brute-forcing you with the likes of Spiritomb, Milotic, Lucario or OMA Garchomp, Kukui's team is much more mundane, yet you can see his team is actually attempting to work together.
Lycanroc leads his team and always uses Stealth Rock in the first turn (thank goodness it doesn't have a Focus Sash). Braviary tries to take advantage of those hazards by Whirlwind shuffling, while Magnezone, Ninetales and the third starter take advantage of Braviary's Tailwind. Snorlax is left as his wincon of sorts, although it lacks a setup move. If you don't use items, your team will already be weakened enough for a Snorlax sweep.
It was a pleasant surprise. Not taking into account somewhat minor facts (Lycanroc is not Sashed, Braviary is not exactly bulky to shuffle a team, and Tailwind does not last long enough), it's a well-thought team for in-game standards, and they did not need to put pseudo-legendaries for a proper final boss, such as Ghetsis (who is only difficult because of Hydreigon's dangerous coverage, and even that is removed in BW2, where he's a joke).