I absolutely love my M&P9c. Someday I'll probably have to add a M&P9 fullsize or a 9L to the stable... I do have a fullsize USP9, as well. Kind of funny you bring those up...the 9c and the USP are the only two guns I own!
My USP is from the first year of their manufacture...1993. It has been completely trouble free after thousands and thousands of rounds and lots of abuse and still on all the stock springs/internals! The mags even still have the stock springs...
Anyway, enjoy your 9L. Let us know how it performs!!!