Initially from peeks and hints I had seen of Altitude, I had thought it would be a cosmic horror story. Alas, it is not (at least not entirely). While there are hints of Lovecraft, it's more for fans of the old EC Comics or Twilight Zone shorts. Indeed, Altitude could be seen as an overly long episode of the Twilight Zone. That makes writing this review a little tough to do without spoilers, as the Zone was known for it's twists (but the films been out a bit so many of you likely already know it's got a surprise in it).
I'll start off with the good stuff: The director does a pretty good job of creating claustrophobic tension, and his monster is pretty darn nice considering the budget most indie horror films have. This is where the good stuff ends.
None of the characters are truly sympathetic, and beyond the main two protagonists they're obvious 2 dimensional victims from the beginning. To some extent that's forgivable as so many films are like that, but whats the point of watching people get offed if you don't care whether they live or die? To be honest their dialogue (and for the lesser characters the acting) actually makes you hope they die. What I find unforgivable was the marketing that suggested the monster was the main bad guy, and a significant part of the film. It doesn't really appear much, and not until later in the movie.
Another major fault is that films really need to hold suspension of disbelief. Obviously you aren't going to encounter the supernatural in real life, but you don't want an audience to roll their eyes watching the film either. There are subplots that quickly disappear or get no resolution, there are too many coincidences that would make even a teenager facepalm, and a lot of the possible plot threads that get introduced are replaced with an ending that feels tacked on. Instead of the cosmic horror I had hoped for, I got teen melodrama. The EC comics nod was nice, but many of those old stories are cliche by now. If you intend to do a tribute to them, you at least need to update them in a way where the foreshadowing isn't predictable.
To sum up, it's flawed. I still recommend giving it a shot (I am an EC comics and Twilight Zone fan after all), especially since it's cheap (the local Walmart has it for 10 bucks). But go into it expecting something different than a monster film, or you'll be disappointed.