If you prefer something like FMA:BTH story-wise, then Death Note is a great choice. These two have next to nothing in common except their awesomeness.
But, if you want some occasional comic relief along with a great plot, I doubt Death Note will satisfy you. DN is rather dark and serious, there's basically no humor in it (unless you count some of L's truly weird quirks and answers).
FMA: BTH is so good an anime that there are very few animes of its genre that doesn't pale in comparison to it. If you haven't watched FMA, try it. It follows an entirely different story line than FMA: BTH, but, is still similar. You could also try D Gray Man, Ao no Exorcist, Darker than Black or Phantom Requiem for the Phantom (This one is way more serious and depressing than even DN). These are the ones that are atleast somewhat similar to FMA: BTH, off the top of my head.
Legend of Legendary heroes too, for some reason comes to my mind when I think of FMA. Its magic instead of alchemy, but can be likened to FMA:BTH.
If you tried and liked Death Note, then Legend of Galactic heroes also will interest you. If you don't like its old art, then there's Code Geass, its new gen rip-off, although CG is a huge failure compared to LOGH.
