It's been confirmed that the episode James first appears on is episode 17, The Garden of Forking Paths, which will air in two weeks' time. The press release is on many sites, here at SpikeTV.
Of even more interest is this link with SpoilerTV quoting TV Guide: a fellow BSG fan is asking about his role in more detail.
MICKEY: How the frak are ya, Romy? Here's what Sonya Walger says about him: "He's this curious person who seems to know an enormous amount about Olivia's future. It turns out that this guy has had multiple flash-forwards, so he becomes incredibly important and significant to her and, in time, to the entire investigation." The bad news: He's not a good guy. In fact, he's going to make D. Gibbons look like a walk in the park full of unconscious people.
Hmm. So he's the villain again? I'm a bit disappointed. I was kind of hoping he'd be more like Lloyd Simcoe - someone with an important part, who's essential to the story without being the enemy, and yet manages to be a bit complex and imperfect.
But let's be honest: some of the show's "good" guys - including Mark Benford, Demetri Noh and Aaron - aren't particularly interesting characters. What's happening to them is interesting, but they haven't managed to get my sympathy throuhgout most of those events. There's something wrong with this show and "good guy" roles, and in that framework, I want to see James as a complex, strange, highly intelligent bad guy. Simon has been the most interesting character for me so far, and he's not really a good guy at all.
What I do worry about is that James is now going to be the bad guy every time, because Gaius was the bad guy. This is annoying because
a) he wasn't, at all;
b) on some shows, the bad guy roles are really black and black evil; and
c) James is such a kind guy in reality - it would be nice to see him exhibit that on shows as well.
But the actors always say that playing the villain or antagonist is the most interesting role. That's the role they want. I remember Jamie Bamber saying that Apollo was a limiting role, because he had to be good, and he sometimes envied James the more varied Baltar. The bad guy gets more leeway.
It's also a question of how James plays the part. He's really only played the eevil villain once, on One Night with the King, where he really was just bad bad bad. (And I doubt that, as a Jew, he'd like to play a Jew-hating bigot with much compassion.) Generally, though, James seems to bring some kind of understanding or nuance or compassion into the part he plays.
The reason actors want to play the villain is probably not that they want to be eevil and swirl their moustaches and cackle in a corner. They want to portray the darker side of human nature, which exists in all of us, but which we usually have to control. It may be liberating to let that part of you go and just get to do bad stuff for once. But if it's not done with complexity and psychological insight, it's just boring and cartoonish.
So let's hope for a complex character most of all, be it a hero or a villain. (Or a weird mixture of both, like Gaius Baltar.)