The best part of the anime for me was always the Pokemon League tournament at the end. It was always the culmination of an entire series, where everything was on the line and where the animators went all-out with some pretty impressive battles. Although some are better than others (Sinnoh and Kalos were fantastic, Kanto and Unova not so much), I always pay attention when that particular arc starts even if I haven't been paying attention to what the anime is doing.
I guess I'd really like a movie to act as a grand finale to one of those series. The animation is always very impressive in the Pokemon movies, which always made me wish that a high-stakes league battle would be the foundation for one instead of a "legendary of the year you'll never see again" plot.
Don't know if a game would fit with that though.