I've read many reviews claiming Guardians of the Galaxy 2 "isn't as good" as the first one. I don't think that's objectively true. Yes, they (or you) may not have liked it as much as the first movie. But that doesn't mean it's not as good. The first installment was a complete surprise. It was fast, fun, bright, and brilliant. Nobody saw that coming, so it exceeded expectations.
Now, a few years later, we remember
how much we enjoyed the original and try to compare our experiences to the last time. Regardless of objective quality, it's very likely you won't have the identical rush of emotions because -- and this is important -- Your expectations are now really high.
I'm reminded of a joke from Hot Shots! Part Deux...
[fountain] Two guys are sitting next to each other, one is reading a book. FIRST GUY What are you reading? SECOND GUY Great Expectations. FIRST GUY Is it any good? SECOND GUY It's not what I'd hoped for. [/fountain]
I think if you go into just about any movie expecting to be surprised and delighted, you're making it very hard to be either of those things.
This is why I try to temper my expectations (and avoid spoilers): to prevent unnecessary inflation of my expectations.