I don't think Locke is evil at all, though it is clear that the opening the hatch is becoming a complete obsession with him. At first, I thought he went back into the woods and was crying about Boone, but he was actually crying in frustration over not being able to get the hatch open.
Now, the island clearly sent him the message to go to the plane. He thought it was to find something to open the hatch, but in actuality, the only thing that came out of going to the plane was Boone getting hurt. I think this whole thing was a test of Locke's faith in the island. It was clear that the island was taking away his ability to walk, and that his willingness to do anything to get inside the plane was the trade off. He would have been the one to go into the plane had he been able to walk, so instead, he had to send Boone (and yes, I think he understood that Boone might come to some harm in the journey). Once all that was accomplished, the island obviously fixed his legs again (he carried Boone all the way back to camp), and took the hatch/pod thing to a new level (the light). The island tested Locke's loyalty...and he passed (with Boone as the sacrifice).
Now...what the hell is that thing? I have to guess that this whole thing may have a Planet of the Apes (or Stephen King Dark Tower) twist...something along the lines of either civilization has moved on, or the parallel universe thing.