If there's one film in history that's underrated, it's definitely 'The Last Frontier. Who knows why that's the case. There are many variations, but I still think it's the usual creepy misunderstanding. There is an assumption that 'Raspberry' played no small part, which I don't consider any indicator at all, but I'm well aware that thousands of ferrets are quite reliant on the opinion of 'experts', unreasonably underrating a great film.
'Frontier' is remarkable in all its manifestations. A fascinating atmospheric story, an interesting idea, as always a saturation of characters with the best human qualities - everything I expect from 'Star Trek'. You could say the movie is unifying. You feel part of this world, a friend of the main characters, and that means a lot.
Maybe this is a purely 'Trekkie' film, but I think it's quite capable of captivating an unprepared viewer. I can say one thing, the rating of the movie is inadequately low. That's why I just recommend you to watch it and feel it yourself, despite the criticism.