I thought it was really good. I personally still like Outcast best just because of the shock value it had going for it. Jedi going crazy are no longer news by this point. That said, it was better than Omen, Abyss, and Backlash. Now, onto the plot!
Tahiri: This was handled extremely well in my opinion. She was sympathetic without seeming like the helpless little girl that she's been characterized as in the past. The trial was interesting and I'm genuinely curious about how it will all turn out. No way she'll get off without some sort of conviction. It wouldn't be right. But I hope she'll not killed or anything. And another thing, what did Tahiri mean when she said she and Jacen were "involved"? I'm having trouble even thinking in that direction without turning green.
Ben and Vestara: Ok, I've been a hater of this relationship. But I've allowed my hatred to cool into disinterest. This is mostly because the two of them having a crush on each other seems to make more sense then it did in Backlash. Although it did move pretty fast, in my opinion. Ben was letting his guard down in his very first conversation with her in this book! That girl must really be a looker.

Ben's internal dialogue of "But I still like her," after he knew what Vestara was up to bugged me too. He'd been given reason to believe that everything she said or done up until that point had been contrived, and he still likes her? *sigh* I also need to point out what is possibly the worst/nastiest comment in recent SW history. Vestara's dad asking her if she'd "bedded" Ben. *shudder* They're what, 16? And who wants to even think about stuff like that in a SW book? *gag*
Jania: While I'm glad she got more page time here and showed some of her old stubborness and determination, the breakup with Jag annoyed me. Most of you know that I'm a huge Smallville fan and this is starting to remind me of the old Clark and Lana rollercoaster of love. Ick. And, Jania, we KNOW you're the Sword of the Jedi. Must you say it every other sentence?
Abeloth/Callista: Ok, I'll admit it. When it got to the reveal, I actually threw the book down in disgust. Once I calmed myself and continued reading, I had admit that it was a nice way of telling us what happened to Callista since Planet of Twilight (anyone notice that one of the more soap opera-y SW books has "Twilight" in the title?) But, really, I hate Callista. Always have. And having Luke remember the feelings he used to have for her like that seemed almost like an affront to Mara's memory. I'm probably just over-sensative, but it annoyed me. And, yeah, the "female presence" aboard the Shadow? Is there anyone who didn't know it wasn't Mara? Creepy. But, all that said, it did make a sort of sense. Now I'm gonna sit here and wonder if she's really dead until Vortex comes out. There better not be any lame attempts to "save" her if she's not.
One more thing, I like the way Mara was characterized Beyond Shadows. I don't know, some of her dialogue in Abyss just didn't seem like things she would say. I think it was handled much better this time. And, even with the whole creepy Callista stalking Luke via the Force thing, I thought Mara had a bigger presence in this book than in any other since she died. I'm always in favor of that.