There are two kinds of movie sequels - let's try to distinguish them. The first kind is when a new part of some movie is connected by one idea with the previous one (for example, the 'Destination' tetralogy: its parts are connected by ideas, but not by plot); the second kind is when a new part of some movie continues the story of the previous movie (for example, 'Nibblers 1-2'). So, the plot of the movie 'Poltergeist II: The Other Side' is a direct continuation of the story, as it turned out, unfinished in the original movie.
And it should be noted that the sequel, although the polish does not reach the level of the first part, but in the statics is still a strong multifaceted movie. Why multifaceted? Well, to call 'Poltergeist II: The Other Side' a horror movie is to say nothing about it. Horror is at the heart of the movie, in its concept, but it's not the main part of it. Like the original, the sequel combines at once the features of both non-banal horror and comedy, and a strong drama with a kind of philosophical subtext hidden in the plot of the movie.
That is, in general, the movie can be viewed from different sides. People who like movies with a strong plot and philosophical undertones will be happy with all the thoughts that the movie leaves after watching. Those who like to cry will shed more than one tear while watching it. Horrormans will not remain deprived either. And those who like to laugh will laugh a lot. Everyone is guaranteed to find something different in this movie!
In general, fans of the original will immediately feel in their rut: the plot of the movie revolves around the same unhappy family as in the original, which continues to be attacked by an evil half-dead half-alive half-dead creature (actually, Poltergeist). The sequel is missing only one member of the family, the eldest daughter, and where she disappeared to is not specified. Well, that's fine, in principle and in the original we almost never saw her. Perhaps the screenwriters didn't know how to insert her into the plot of the sequel.
If we talk about the plot component of the sequel in detail, the main thing that should be mentioned here is that the sequel develops, as it always happens in normal sequels, the concept of the original movie, bringing it to the point and answering some of our questions left after watching it. However, it's a matter for the fan: not everyone likes when the concept is brought up to speed by the authors, because some people really like to make up their own minds for the authors.
This is the main problem with any sequel that develops the original concept of the movie. The audience does not like that the authors make their point of view about the concept of the movie official by releasing a sequel, hence the perception that the sequel is always worse than the original. But that's not the point. The most important thing is that when the concept of the movie is thought out and fully thought out from the beginning, then all the other parts of the movie are based on the same concept, that's why the audience gets more pleasure from watching a 'complete' movie ('Lord of the Rings', for example - J.R.R. Tolkien released three books at once). But the same 'Harry Potter' is the most ill-conceived saga I have ever had the distinct honor to get acquainted with, because every next part of the book (and later - the movie) is equipped with unexpected details about the universe; it is immediately obvious that the author's ideas on the development of the universe appear on the fly, but it's wrong, you can't do that - it's much more interesting when everything is already invented initially, but we get acquainted with it gradually (again, 'Lord of the Rings'!).
Verdict. 'Poltergeist II: The Other Side' is in general a good movie and, in fact, a strong sequel, but here it's a matter for a fan: yes, the sequel accumulates all the best that was in the original, but it also develops its concept, which not all people will like. This is the only significant disadvantage of the movie.