This is the best river cruise i have ever had. The reasons are simple :
1. Most of the beautiful views of London are covered
2. The tour guide is amazing - Vicky, our tour guide as very upbeat and told us a lot about the story behind each and every sight we saw on the cruise
3. Economical - I took the combo of river cruise and standard london eye ticket and paid some 32 euros for the same.
I would highly recommend the river cruise if you have very limited time in London. London eye is decent but not must experience.