It was a very enjoyable episode! I still like "The Christmas Invasion" a bit more, but this was very close to beating it.

it almost makes me think he might go companionless for the season 5 specials and just meet someone different in each one. i haven't read any spoilers on s5 so that's just pure speculation.

I'm not sure whether or not they've announced casting information, but based on this episode, I would agree with you.