I decided to ride The London Eye this visit so I could quickly get reacquainted with this vast city and plus, I had never done it. It's one of those things where I mentioned it to people living in London and they said "Oh I've never done that," like New Yorkers and the Empire State Building. My biggest tip-buy the Fast Track ticket so you can avoid the masses of school groups.
Half an hour is just the right amount of time to be in the air and I'd go when it opens on your first day in the city to get the best overview and shortest line. The views of Buckingham Palace, Westminster Cathedral, St. Paul's, and the Thames are worth it.