Great job with the exposure. Settings look good. I snooped in the EXIF a little bit, and wow, that's about the best you can wring out of the ol' XTi. Really nice work in the noise reduction too, I would not have guessed it was 1600ISO on the XTi... that's really pushing that little guy to its limits.
Based on the catchlights in the eyes and the shadow on the wall, it looks like a hotshoe flash (maybe with a small diffuser?), mixed with a little bit of ambient/room light source - so nice job with that, it doesn't have that "deer in the headlights" look that one can get by trying to blow away all the ambient with the flash.
Good job getting the focus on the girl's eyes, but with the guy standing behind her, it looks like his face falls a bit out of the plane of focus. You MIGHT have been able to close down the aperture a stop and crank up the flash power a stop, but that's really pushing your mix of flash and ambient. A better solution might have been to give gentle direction to push her back a bit and lean him forward over her shoulder, to put their faces both in the same plane.
I would have really liked to see a more dramatic pose or at least some more intense facial expressions... but posing others is tough, especially giving direction to random strangers at a con where you only have fifteen seconds to build a rapport. It's also tough to direct "characters" that you're not familiar with, but they may have known some better in-character poses than just "stand there and smile."
If you're using a flash, don't forget you can "drag the shutter" to use a slow shutter speed and still freeze them with the flash. So you could have them moving, swinging their blades, etc, and when you pop the flash they're frozen. Set the flash to 2nd-curtain and you get a small ghost trail leading up to the frozen pose. So, you may have been able to get a more dramatic, action-y pose by doing that. But, if their props are falling apart, that might not have been feasible.
Anyway. Great work wringing the best you can get out of the XTi. Technically, it's quite good, but a more dramatic pose and facial expressions would have really taken it up a notch.