LOI is certainly loads better. People above have mentioned the music and atmosphere, which I like. And sure, the level designs may be bland and all too same-y, but so are COD's, and sadly, COD's diversified and all-too-big level layouts are even more boring.
LOI I actually had fun with, and even played through a few times. It's not great by any means, but it's enjoyable, despite all its many flaws. COD, on the other hand, I've owned for a couple years, and I still haven't beaten it, because every time I pick it up, I get so terribly bored. It's one of the worst games I own.