To my suprise this was way better than the Butterfly Effect 2. I was actually starting to get scared off watching this one because of the second, but in the end it was quite good. The story starts right in the middle but you get the idea of what is happening. It's good as a stand-alone movie but it probably shouldn't have taken The Butterfly Effect 3 as it's title.
It's more gorier than the first and second put together. The deaths can be quite shocking, especially the opening scene. The "condition" rules in this film arn't the same as the first one, like the second one wasn't the same as the first one either.
But give it a chance. Don't let the rubbish second one scare you off. I don't want to say much about the movie because it might spoil it a lot (in my eyes I think it will) but this is way better than the second one.
I don't expect any "yes, this has helped me" or "no, it doesn't" but just give this one a try, it's quite good and brings the Butterfly Effect series a good name after the dreadful first sequel. You don't actually have to watch the first two to understand this, it's a stand-alone film like I said but just give it a try.