Comedy sequels are hard. Just think about how many struggle; not financially of course, because people will show up in hope, but just think how many get caught between recycling the jokes of the original and needing to change it up, leaving them caught on an unfunny hook. I'm not sure Pitch Perfect was made with franchise in mind in the first place - it's a pretty complete film, character wise - but it was a big hit and so the sequel needs to find somewhere new to go. So it tries to go up and down at the same time; tearing down the team to they are the underdogs once again, but also putting them on a larger, more ambitious stage.
After their triumph at the end of Pitch Perfect then, we open with a trimphal tour, playing to large crowds including President Obama himself. Only hubris and ambition get the benefit of our heroes, and after an "incident" they are cast out into the wilderness, with the only way back to win the International competition looming in Copenhagen. The film does introduce some rivals for this - a stereotypically efficient German team - but mostly the conflict is internal, and the Bellas have to work out their own lives and loves before pulling together for a big, predictably heart-warming final.
Pitch Perfect 2 definately does the sequel thing of revisiting a lot of the big notes of the first film. The musical duel returns, most of the character beats are familiar, and things you liked about the first one are all present and correct in the second. It does manage to avoid some common pitfalls; it doesn't undermine the character work of the first film, for example, but rather carries them forward, and even the stuff we're familiar with like the commentary team are still funny and fresh from being used sparingly. Yes, there is some sense of diminishing returns, and the newcomer character especially doesn't seem to get a lot to do, either.
But there is a very solid base here - the cast are charming and funny, and the script sparkles in the right places, and the musical performances are excellent. Some of the surprise is gone, of course, the sense that this is perhaps better than it has any right to be, whereas now you expect this to be good, and of course, it is. Not as good, perhaps, but still good in it's own right. There will of course be a third film, dangerous waters for a comedy franchise, but as things stand I'm still looking forward to it!