"I thought Hans Peter Janssens was actually kind of static and creepy, with his big eyes. Gorgeous voice, though. "
I disagree about the static and creepy, but agree with you on the gorgeous voice, I thought Janssens was much better than his predecessor.
I concur with the others who recommend Evita -- well worth a visit.
Also, to clarify my comment on the RSC and MERRY WIVES, the performances will take place in Stratford-Upon-Avon, about 2 hours or so from London via train.
Blood Brothers is a London staple, I'd definitely recommend it. Just don't see a matinee, that's when busloads of school kids come.
Woman is Black is a great play, creepy, scary, and VERY cheap. Sorry to see Bent closed, I saw it last month and was blown away. Guess it's too uncomfortable, unlike Mama Mia or Wicked.
WWRY is a lot of fun. I took my sister to see it, who isn't a big queen fan, and she loved it.
Wicked I'd skip, unless you're one of those people that eats, sleeps, and breathes it. Getting in and out of the theatre is an experience in itself, absolutely packed to the gills. You can't even move because both entrances are like shopping malls selling everything Wicked related.
Just be sure to buy your tickets in the TKTS booth in Leicester Square, or the theatre itself if TKTS doesn't have them. Do not, I repeat, do not EVER buy them from those other ticket outlets in Leicester Square. If TKTS doesn't have what you want, take 5 minutes and walk to the theatre to get them, you will save TONS of money, and know exactly what you're getting before you fork out money for them.
The only other booth I trust is the one in the entrance of the London Hippodrome. That's not to say all the others are dodgy (look for the 'STAR Registered' signs) but they may not be selling the best tickets at the best prices...
I'd say see Woman in Black, Blood Brothers, Billy Elliot and Evita. Things you can't see in the US.