I'd suggest that viewers watch 'Limbo' on DVD with the voice-over narrative by John Sayles, the director. A lot of insights provided there, including a lot of little details which give you insight into movie-making--the reason for multiple takes, visual effects, the importance of 'continuity', and even a lot about sound, which was a big issue in the making of this film.
I was amazed to learn that Mary Elizabeth Mastrantonio is such a terrific singer--she sang all the songs and, in fact, her voice was recorded live while shooting the scenes, not dubbed in later in post-production. Sayles describes this in his narrative.
Sayles had less to say in the narrative about the ending, but based on the comments he DID make it was all quite intentional--not the result of studio politics or a screenwriter (Sayles himself) who couldn't decide on a final ending. In fact, I would suggest that it is Sayles' standing in the business that permitted this film to be produced & released without answering the question of what becomes of those characters, though it also occurs to me that it could be the reason why this film didn't get much of a marketing push. Clearly the audience is left hanging in--dare I say it--a state of limbo. Sayles has no intention, based on his comments, of a sequel, though he invites anyone else to dream one up if they wish.
But aside from all this, it was a terrific film, with interesting characters, shot in unusual and often stunning locations ("Insomnia" comes to mind when thinking of recent films shot in Alaska with its scenic backdrops).
The cast was generally quite good--Mastrantonio and Strathairn were terrific, and Kris Kristofferson was a great choice as the likable but edgy local, Smilin' Jack Johannson. Vanessa Martinez was, for me, less convincing as the daughter until the boat trip and beyond, but that is when her character becomes truly important to the story and her work was quite good when it mattered most; up to then it was all teenage angst.
Overall, I enjoyed 'Limbo' a great deal, and the limbo in which the audience is left with such abruptness was, for me, almost a slap in the face--a welcome one--in striking contrast to the 'Star Wars' series in which George Lucas took 6 movies and nearly 30 years to tell us how Darth Vader came to be.
Note: I am NOT slamming Lucas or 'Star Wars' by that comment, only making a point.