The grenade was a tad too far for Locke.

The actual change happened within days of being on the island. He's just evolving into the role of "island protector" now, which isn't that much of a stretch from the guy who delivered Boon to his death.

He really annoys me! Ordering people about the way he is! it isn't his island or his colany of people! Grrr!

since he was encountered by tall ghost walt/jacob, he was ready to kill himself but then i think he was 'reborn' when he saw ghost walt, if you remember in season 1 jack and locke were propa buddies, locke saving jack an all, on the island its only been 60days since locke saved jack so to repay locke, jack decides to pull the trigger, lolz.

lol, i dont know wut to pick!!

Locke seems to swing in two directions (not like that, cheeky)

season one he was finding his purpose, and mr nice guy locke.
season two he found a purpose and 100% threw himself at it which didnt turn out for the best, and we have a bad ass* locke
season three and locke is looking for a new purpose and he appears to be back to mr nice guy locke
season four he has discovered a new purpose and he's throwing himself at it again and is turning into his old bad ass* self

we dont see much middle ground with locke. he just bounces from one side to the other...

*for lack of a better word on a family friendly site

I don't think he was meaner, but he became kind of dumber since he got more control of the people. It's like the responsibility made him realize he had no idea what ha was doing and took it hard.