A few threads here mentioning Johto starters in unusual balls reminded me that Pokémon Colosseum exists. When I bought it many years ago, I never played it for more than an hour—maybe I didn't like the double battles or not being able to transfer my Gen III Pokémon, who knows. And so, a few days ago, I decided to give it another chance.

I kind of like it. Fighting only double battles feels refreshing and gives battles a different dynamic, and the grungy (but also ugly) environments an interesting change of scenery.
The animations for some of the new Gen III Pokémon are amazing (Zigzagoon, Spinda, Kirlia, Surskit, Slakoth, and Metitie come to mind); a shame they merely recycled the Pokémon Stadium models and animations for all the older entries.

The biggest downside is probably that you can only save at PCs. Since you can't turn animations off, and you don't have access to many sweepers (nor moves), battles take a while as it is. Catching Shadow Pokémon takes even longer, and since you don't get another opportunity any time soon, I usually run back to the nearest PC to save afterwards, which breaks immersion a little.