Insomnia (1997), original release.
This version stars Stellan Skarsgaard, who is remarkable but really quite different than Al Pacino in the remake (Christopher Nolan, 2002). In fact, it's really an interesting study between the two movies because they are both viable in their own rights led by a great actor, besides some flaws in each story and each still managing to share MANY of the same plot points while using them in different ways.
Put simply, the American version allows for the flawed protagonist (there, named Will Dormer) to wrestle morally with his actions and sets things up so that his flaw is more a choice between "goods" (integrity vs pragmatism); this also means that his flawed choices are driven by a system outside himself. The Swedish version doesn't really offer a compelling external reason for Jacob Engstrom (starring protagonist, different name) to lie about his mistake, except that he's already been in trouble once for past indiscretions and... his professional ego seems fragile. So here, it's more a matter of watching Engstrom act amorally mainly to cover his own tracks, yet find himself in more and more of a tangled web where each lie demands another lie; and the only sense that it bothers him at all is via some pretty nuanced by effective facial expressions on the part of Skarsgarrd (who can do a lot with a little) + his inability to sleep as the penetrating eternal sunshine -- like a blazing conscience -- keeps him from sleep and eventually drives him into hallucinations and short reality breaks. Whatever victory he finds is ultimately hollow.
tl;dr -- Dormer is threatened to be driven over the cliff by his own moral compromises for a greater good + external events; Engstrom drives that puppy right over the cliff on his own because he doesn't want to ruin his professional image.
One point of comparison between the two (that tells you a difference in how the protagonist is portrayed) is the dog. Without explaining too much of the scene, the dog is handled differently in each version even if it plays the same purpose, and one character is much colder than the other in what unfolds.
Another key difference is the villain. Same basic guy, same basic stuff... but Nolan's version (where Robin Williams did a solid if sometimes a little too verbose job in the role) is actually actively pressing Dormer, initiating their relationship, overtly rationalizing his behavior. This all fits in with Nolan not just positioning Dormer as a struggling (versus corrupt) hero, but also his highly accentuating the sunlight issue in his version (since the baddy manages to also interrupt Dormer's sleep the few times he starts nodding off) -- the original movie kind of plays it straight in that regard. Both versions of the baddy operate from the same basic angle, but the remake's version makes him more more a harrier of Dormer and perhaps even perpetuating his murder cycle (thus needing to be stopped by hero), while the original's version seems much more interested in simply being left alone and it's not clear if his performance would be a repeat. Dormer's behavior is thus more justified script-wise than Engstrom's, building sympathy.
Culturally the differences could also reflect upon Swedish understatement versus USA overtness. The USA has a few more action sequences that seem appropriate, even if the gun battle at end is a bit forced. it also has a few artificial peaks that can make it feel forced + an emotional undercurrent (where you emotionally can connect with some characters) that occasionally feels the same; the Swedish version is flatter and could have used a little bit more to break up the emotional monotony but offers a more cynical and clinical view of the "hero" and you're mainly watching his dissolution, which is also an interesting approach.