I felt the same way, he could of waited since the zombies were not even that close. Or at the very least he should have shot Odis in the head, shooting him in the leg was a major dick move
Seriously.. Odis did everything for Shane
1. Helped him through the school
2. Jumped off the bleachers in the gym which distracted all but 2 zombies away from Shane
3. SAVED HIS LIFE, from the zombies near the gate
4. Helped him run from the zombies because of Shane's leg
Overall Odis is a badass, aside from shooting Rick's son.
If he shot him in the head it would've been way more practical. He could still be eaten by the walkers, he wouldn't have screamed, and there wouldn't have been a struggle when he was trying to get away. Maybe he wouldn't have felt as bad about it either. Shane is starting to really grind my gears, and also Andrea (I think that's her name.) I wish she would've died along with her sister :|