It's a good movie if you don't mind the Giant plot holes

Rating: 8/10 (11 February 2008)

If Marty and Jennifer left in 1985 to go to 2015, it would not be possible for both Jennifer and Marty to exist in 2015 since Biff mentioned he never seen a Delorean for 15 years. This means Marty and Jennifer just changed the timeline. The other problem, but not a serious plot hole is him giving the Almanac to his younger self in 1955, which a future has changed, the old Biff should disappeared or something. One exception of not changing the future if going to the future is to view Marty and Jennifer of the future, without physically going there would not have that effect. The original Time Machine movie the man left in a time machine and he was not there in the future, and this made sense. Nevertheless. Back of the Future II is my all time favorite, because of it's intriguing plots concerning changing the future.