About as believable as any good zombie film, Isolation excels at pacing, thorough examination and explanation, and coming full circle with all of the concepts it presents. Something that so many similar movies fail at.
If you are looking for a mindless slasher, watch something else, though there's slightly creepy nuances that beckon back to films like Alien. If you need that human relation-based plot, there might be enough here to keep you satisfied, but the film doesn't rely at all on developing side-stories of love and emotion. Characters have seemingly realistic reactions and make understandable decisions (unclouded by the need to make irrational decisions for the sake of building tension in the script). Scenes follow-through to conclusion and don't seem edited for time.
Isolation leaves no main plot thread unresolved, and stylishly elaborates on the scientific as well as horrific ideas as they presented. I don't think this will be a widely appealing film, but it didn't take any wrong turns. I don't recall any advertising for it. This might mean it's less Nike and more sandal, but there is a time when sandals are practical.
It's every bit as intelligent as the best X-Files episodes, and I wasn't able to find any cheese in the effects, though I half-anticipated it to devolve into Critters or a Texas Chainsaw movie. It didn't, however, and was able to maintain it's integrity throughout.
I thought it was a gamble when I chose to rent this over a well-advertised title. But I now feel it was entertaining enough and well worth picking up.