John Carpenters 1982 re-imagining of 1951 movie The Thing From Another World sees a team in the frozen vastness of the Antarctic falling victim to a shape shifting alien parasite. It can look like anyone, it can take them over and hide within their flesh leaving them outwardly intact, and it isn't friendly.
Packed out with memorable scenes - the dogs, the spider head, the head to head dance of death to name but a few - the special effects still look pretty great today. They're executed well too, delivering jumps and tension aplenty, the fear of the trapped men is contagious, their terror and despair is ours as they turn on one another and try to battle an alien foe who could be any one, or all of, their companions. Perhaps, unknown, it could even be themselves.
This takes the enemy within paranoia so common in the 50s sci-fis - could your neighbour or friend be a commie pinko sympathiser, plotting, the enemy within? - and brings it bang up to date with the gloss of a great director, talented cast, and top notch visuals. As already mentioned, the effects are great, and they've aged well - even where the age shows through, the feeling is they've matured gracefully and grown fonder with the passing years.
Pacing is spot on, the atmosphere of panic is infectious, it's one of those classic movies that deserve a proud place in any fans collection. Then again, you already know that, you've bought it - right?