The society that Jonas lives in has a lot of great things going for it. There is virtually no crime, no hate, no anger, and there is no sadness. The society is also an incredibly well-functioning society. Unemployment doesn't exist, and people are given jobs that they will both like and do well with. The weather is controlled, so something like a cataclysmic natural disaster can't wipe out people or structures either. There are a lot of reasons to like and admire Jonas's society; however, there are some negatives to it.
A lot of readers point out that Jonas's society has essentially gotten rid of choice. I don't completely agree with that. Yes, there are a lot of rules that govern when people are allowed to do certain things, but that isn't any different than present day society's rules about voting, gambling, and driving. I'm sure many parents also have rules about when a child is allowed to have a cell phone. The society does choose what somebody's career will be in, but that person did get to choose where most of their volunteer hours would go.
In my opinion, the single greatest negative to Jonas's society and taking on the Sameness is that emotions have been removed. I will freely admit that I don't like feeling sad, depressed, angry, and so on; however, I know what those feelings are, because I know what it is to feel happy. Conversely, if a person never experiences sadness, that person can't actually know what happiness feels like either. Jonas's society may be a functional society, but it is an emotionally dead society. Just because the people are not sad doesn't mean they are happy.