I believe the play-like feeling can be attributed to the fact that 90% of it was filmed in front of a blue screen. Considering all the goofy camera tricks used

I believe the play-like feeling can be attributed to the fact that 90% of it was filmed in front of a blue screen. Considering all the goofy camera tricks used to make the characters look proportionally correct, is must be very difficult to act in that kind of situation and have it come off feeling natural. Props to Andy Serkis for rising above the rabble.