Unlike most anime/games adapted into manga, it actually lasts more than two volumes, the original artist is involved, and it keeps the same general plot while basically being a more extensive "director's cut". So yes, it's worth it.
What the hell is the point of those "anime adaptation of manga" that never had any detour from the manga?
I'll tell you why: music and voice acting. Death Note just wouldn't be the same without that awesome music. I'm glad I watched the anime instead of reading the manga.
