This is a decent adaptation of the PLANET HULK graphic novel, streamlining the book and making it accessible to those who haven't read it. Earth's heroes, led by Iron Man, rockets the Hulk to a distant, uninhabited planet because they deem him too dangerous to remain on Earth. But the Hulk damages the spacecraft and veers off course, so he's sucked into a vortex and crash lands on the desolate planet Sakarr. He's captured by these red humanoids, who are ruled by the Red King, and taken to the coliseum where he's to battle for the city's entertainment. He defeats one of the planet's most fearsome creatures, this Godzilla-sized squid monster, which impresses the King.
In the pens, Hulk is introduced to the other slaves, who include Hiroim, a grey skinned humanoid, Lavin and Elloe, red skinned aliens deemed traitors, Korg, a rock-like creature and Miek, an insectoid creature. And then there's Caiera, who is the Red King's bodyguard. She protects him because she believes he's the Sakarr-son, the savior of their planet, since he and his androids showed up just in time to stop the Spike War, which happened years before. The spikes are these spore-like creatures that infest your body and turn you into these spiky zombies. But when she learns that her king is anything but a savior, she switches sides and helps the Hulk, who seems to have finally found is place in a world.
There's lots of fighting, multi-colored blood (depending on the alien) and it's great to see a relatively intelligent Hulk who can speak instead of just screaming "Hulk smash!". This movie is one of the better Marvel animated films.