Saw this the other day (as much for preparation for the ACW campaign as anything else). A bit slow in parts (but I suppose they had to get all the key elements in and how each commander felt etc.) and also a bit heavy on the swirling 'grandeur' music ("Yes - its an important battle in American history - we get it!") but excellent when it got down to brass tacks and the battle scenes took place. I defy anyone to watch the defence of Little Round Top without a tear in the eye and a lump in the throat. Similarly the action around Pickett's Charge as Lee tried to take the Union centre was superbly filmed. You can't believe that commanders would walk in front of their men (making them perfect targets for sharpshooters) and that the men would walk (walk!) a mile in daylight under the shot of cannon and musket - climbing a high fence just in front of the enemy (who held the heights and were behind a stone wall).
So a bit long and a bit over the top in the depiction of key scenes but generally a very good film and a great depiction of a major battle.