I really did not like that they used the same exact plot. The structure being the same is fine. Ongoing jokes that carry over are great. They literally copied and pasted the script over, changed Vegas to Thailand, and changed probably ten other words in the entire script, that's how similar it was. Way too similar for my tastes.
It had a some hilarious parts. But overall, way too similar to the first. It was a remake IMO, not a sequel.
Would this movie be great if Hangover 1 didn't exist, absolutely. But it was 99% same exact material, it disappointed me quite a bit.
My grade, C-. Loved 1, 2 was less than impressive.