It's not nostalgia.
Team Rocket was the most effective CRIME SYNDICATE in the pokemon verse. Let's be real. Giovanni really was the Godfather of this series. Don Corleone at his finest. It makes SENSE for a reasonable, bottom-line oriented thinker to run a game corner as well as other businesses all the while growing an empire.
What's scarier? EVIL bad guys with control Legendary pokemon (which will ultimately be restored by the balance of power among 3 opposing Legends with or without the help of the hero) or an incredibly shifty pokemon mafia that has been lining the pockets of officials and politicians for years, whose power has yet to be challenged and is basically playing puppet master to to the entire plot up until the Godfather is taken out. (Don't get all nit-picky on me here. I know this is a stretch. But the Godfather metaphor is a legitimate one).
My point is, it's a very different sort of "villainous team" but frankly, more insidious. I don't think anyone is questioning Cyrus as the ultimate BAMF of the pokeverse, but Rocket had him beat as far as organization and planning were concerned. Giovanni would have succeeded without Red. Would Cyrus? I don't know. Giratina wouldn't have any of that I'm sure, and if he did, raise your hand if you think Arceus would just roll over for him? I didn't think so.
Yes, I'm glad Team Rocket will be returning. I think there are the most realistic of the teams, and therefore the most frightening. They're only problem? Giovanni needs to do a little more background checking before hiring his grunts. A good mafia would have never let a kid even see the boss. Pop a cap. Steal his pokes. Done. :)
