CODA is the system and source books of LOTR which are mostly based on the film versions of the books, released in 2002 and onwards..
Merp is an older system based on the original source material, and there's allot of it! Not having owned it, i am basing my statement on my friends who do, but it has some extremelly accurate, detailed, and in depth multi-page source books that detail one end of Middle Earth to the other.. but the system is pretty awful
If you like CODA then there is nothing stopping you from using the excelent maps/ source material from the original MERP as a source book for adventures.. CODA is a pretty simple system to adapt to your own material / view of the world.
That said the films diverged slightly from the world as wrote, so you may have to fudge your way through any differences.