Obviously it's going to the show a lot of stuff about his wild youth and his various indiscretions (drunk driving, skipping out on national service and son on), but it's the truth and it's all part of his life story, so it would be irresponsible and biased to not show it.
In all of the things I've read about this movie, Stone has stressed how he is not attempting to condone or condemn Bush, just present the events. I for one am incredibly interested to see how this will turn out, as I find Dubya's journey a fairly intriguing story. It's just a shame that it's real.