...I hate that OP.
I kinda like it.
I mean, sure, it's not We Are! but it's an appropriate opening for celebrating the old and ushering in the new, especially since at this point in the time skip nothing heavy has happened yet. There will be time for more exciting or more angsty OPs (though the latter is hardly One Piece's style in terms of their openings or their endings), but for now, it's pretty suitable.
@Osayidan: I found the fake Straw Hats to be a perfect representation of how far the actual Straw Hats have come in two years. Not just because they're imposters or it allowed us to see some of the new abilities and mindsets of the crew, but because it's kinda like the entire crew saying "Wow, you guys are still on that? That was so 2 years ago," showing that even in their lull period for training, our beloved crew remains trendsetters on and off the Grand Line, for those behind the times and for those ahead of the curve.
Plus, it's totally something Oda would do. That crazy, random shounen genius.
But you're right. It's not something that should be dragged out too long. Although I will say that we should probably expect some filler either now or after the conclusion of the Fisherman Isle arc. The anime might only have a year tops before it catches up with the manga if they don't throw on the breaks. Even less if they decide to be trigger happy with hour-long eps.