Insurrection shows the uniformity of standards that is a hallmark of the TNG movies: If you want to know what it scores out of ten, average what you would give the first two TNG movies and that is the score.
The plot is easy to get from the web site, http://insurrection.startrek.com/, so I shall not repeat it here. It would please Mr Roddenberry (as Marina Sirtis points out in a comment on the web site) that the story involves "standing up for principles", and generally moral sorts of things. The theme revolves around ageing, which is one of the all-time winners for drama after messiahs and love triangles. If anything there is a bit less shoot-em-up-ism than one might expect. There are interesting sub-plots: the federation is noted as being in a weak state; Troi and Riker are set to recommence having it off; Picard finds a woman who neither dies, nor turns out to be a villain, and who is contrived to be gorgeous, resourceful, and 300 Earth years old (he likes older women). While she does not leave the Garden of Eden for him, and he will not be giving up his commission for her, he does have over 300 days of shore leave owed, and every intention of spending it with her, and she can slow time....
F Murray Abraham was superb, and in the part of a revengeful alien, a hard role to deal with at the best of times. Kay says he was "unrecognisable" but I knew him instantly by his voice and eyes; he must be a very powerful personality in the flesh.
Criticisms include the usual ST atmosphere of "let's get the gang together and have a lot of fun making a movie", the World-War-II-movie way of dealing with fights and technological solutions, and Riker's acting. On the plus side to enhance your viewing pleasure, there are a few pieces with a strong sense of humour (e.g., Worf's zit, Riker's beard, the smooth-as-an-android's-bottom and the bath scenes), and a passable depth of characterisation for a sci-fi, simple-morality, plot-flick.
Don't race out and see this, but get a group who like TNG, have at least one drink before going, and see it on a big screen. It's not a lemon.