Lexapro (Escitalopram) and Celexa (Citalopram) are different medications, but they are "cousins", and are very similar.
There is nothing Celexa works for that is better than Lexapro, and vise-versa. What makes one work better than the other is their own body chemistry. For some people, Celexa works better - and for others, Lexapro works better.
Lexapro does not have a generic version right now, and it's pretty expensive. Most insurance companies want patients to try Celexa first (actually the generic) and if that doesn't work, they will approve Lexapro.
I tried Celexa, and it did not work nearly as well for me as Lexapro - but that varies from person to person. I do not have insurance, and paying the difference is well worth it to me.
I hope that answers your question...