I was never a big fan of the Face of Boe. He's basically a giant head in an oversized aquarium, so it's hard to take him seriously. Still, it's a testament to the show that they can still make you care about what he has to say. ("You are not alone." Tingle!)
Also...the Macra! The Macra were last seen in the 1967 serial "The Macra Terror", with Patrick Troughton as the Doctor. Unfortunately, that one was lost to the great Beeb video wipeout a few decades ago, so we'll never have the chance to see how 1967 BBC effects personnel visualized giant, sentient crabs. I'm going to guess there was a lot of papier-mache and some quick cut-aways to reaction shots.
Anyway, I love when the new Who features things I recognize from the old series, even when it's little stuff like the Macra, or the Autons in the very first episode. It makes me feel extra dorktastic.