I think Cosima feels like she's being held back because she's unwilling to let herself get caught up in the drama of what's going on. Right now she's more interested in putting the moves on her moniter.
For what it's worth, I feel your comparisons of this show to Who are a tad unfair. One show is aimed at a wide audience and one is pretty adult. As for the finale feeling incomplete, well this is the first time I think that the finale was just set up for a special. So yes it may feel incomplete, but that's because it was being used to set up story elements that will be fully explored in the fiftieth anniversary special.