I like how hypocritical Jacen's become.
"there is no dark side...but I can still become a Sith!"
But more especially his "sacrifice".
Let me see if I get this straight. In accordance with some whacked-out "prophecy" that Lumiya most likely made up herself, he has to go kill that which he loves to progress in his training.
But he doesn't want to kill his wife/child, so he decides to kill his aunt instead, due to some logic that Ben'll hate him if he does it, and that's good enough.
Seriously, what? If he isn't willing to kill what he loves most, then he clearly didn't live up to his "sacrifice", which makes the entire exercise pointless. If you're going to turn to the Dark Side, go all the way, don't just compromise. "Well, I'll kill this relationship, which is almost as good, though not quite." It's like deciding that you're going to go on a diet by eating only three doughnuts a day, instead of four. That's not much of a sacrifice there.
The excuses he comes up with to explain away his stupidities implies that he's really just inconsistent -- of course, since this trait has been exhibited by both of his more recent 'teachers', I guess I can't really expect anything else.
His current portrayal is quite frankly pathetic. At best, he's a bad Vader clone, minus any of the obvious character development that led to his downfall (Anakin, at least, had a history of not letting go, but looking at Jacen, it's like he decided to go turn to the Dark Side at random). He had Anakin's own history, in a similar situation with a greater manipulator (Palpatine), and he still couldn't tell the obvious. Even though the wannabe Sith herself told him that "everything I tell you is a lie", he still didn't get it.
The only way that this could end well is if he becomes a Vader clone in form as well -- I'm thinking, Luke chops his arms and legs off and Solo ends up in a suit. It would be cheesy, and cliched, and repetitive, but it's not like anything else about the story isn't, and it would serve the brat right for not figuring out what's going on, despite the fact that it's in plain sight to people who have similar information about the situation (the readers).
I liked Jacen before he was being written as an idiot, but nowadays, I basically hate his guts. I'd be happy to see him die.