I've not kept up with this season of Dr. Who. I'm not a big fan of David Tenent so his Doctor doesn't particularly appeal to me. I've have managed to see parts of some of the episodes (including the Pompeii one) but can't say the the new companion (Donna?) works at all for me.
For a companion to work there should be an undercurrent of sexual tension between the two. I don't think an actual romantic relationship would ever actually work for the show, but you have to make the audience want that.
I don't see that here at all. The best that I can see working currently is a bickering brother/sister dynamic. I can't see Donna as even remotely romantically interesting.
I'll admit that the fact that the woman is at best 'plain-looking' might have something to do with it, but I've also found her personality abrasive and annoying, but not in the endearing way the Lois started out.
My all time favorite companion still is Sarah Jane Smith and probably always will be. Of course, she was the companion when I first discovered Dr. Who.
Tank (who is really bummed that the 'Sarah Jane Adventures' is a kid's show so he can't watch it)
