Unlike letica! and ForgivenForSure I disagree and think that The Butterfly Effect was an amazing movie that defiantly breaks the mold on time-travel from Donnie Darko. Donnie Darko shows one thread of time travel and doesn't really expand on it and you don't get to understand the full meaning of traveling back in time and how one thing can change everything. The Butterfly Effect shows this fully, how changing one situation can change your whole life. Anyone who says the plot didn't make much sense needs to sit down and watch the movie again and really think about why everything happens.
Overall a great movie to see, but one you will have to think about while watching, however the feeling of figuring it out at the end is truely amazing. A must see.