These changes were, of course, made to increase the dramatic tension in the film, which it does. Since they don't materially alter the overall story, I'm fine with them. What the film is extremely accurate on is the recreated Apollo craft, which according to those in the know, is almost an exact copy. The astronauts' space scenes were also filmed aboard NASA's KC-135 anti-gravity simulator aircraft, also known as the "Vomit Comet". This is obviously more realistic than putting the actors in harnesses on wires, which was the original plan. Apparently the plane lived up to its name when one of the cameramen threw up all over Bill Paxton.
Finally, what I also enjoy about Apollo 13 is that it shows not just the dangers inherent in space exploration, but the wonder of it as well. We humans tend to become blase about miraculous things very quickly; as we see early in the movie, even at that time, comparatively early in the days of space travel, a trip to the moon was treated as no longer very interesting- until, of course, disaster struck. But when the astronauts look out the windows in awe at the sight of the moon and stars- and earth- I am reminded of the feeling of, as a child, laying on the roof of our shed back home on a summer night, getting lost in the beauty and wonder of the night sky.