that's definitely a different perspective. your description of the L3000 sounds closer to how one may view the HD650.
it really sounds like the L3000 is not your cup of tea. it seems like you prefer a more forward and somewhat bright punchy sound, which is a grado, and i suppose with a better soundstage is the AD2000.
so what in your opinion - music or qualities - does the L3000 excel at, if anything.
To answer your question, I think it excels at Jazz, acoustic and bass focused music like for example Drum and Bass (Concord Dawn and High Contrast just to name a few). I think it's pretty good with any sort of music that has a sense of air and space. There also a few lighter rock recordings I like with the L3000, but those are mostly well-mastered and bass light recordings.
I've come a long way from being a basshead (EQing my DT911 to be an extremely bass heavy can) to now preferring bass lighter and crisper sound. I've been a former HD650 owner but preferred the AD2000 in the end.
A few months ago I've begun to develop some sort of fatigue when listening to bassy cans. I can't really say why that is, but somehow the L3000 pronounces the effect and it makes me either turn down the volume massively or stop listening to music because I feel somehow uneasy or nauseus. There are days when it doesn't happen and I don't get annoyed by the bass, and there's those days when I grab some bass lighter cans instead.
So yes, I prefer quick and punchy bass over (even marginally) boomy and slow bass.
The fact that I don't really like the L3000 most of the time for metal is mostly down to my preference and to my recent intolerance for bassy sound.
Leaving my personal preference aside, I think that Metal doesn't really need the amount of bass the L3000 produces to sound good, the AD2000 just sounds more "right" to me. It renders kickdrums with a nigh perfect balance of weight and attack. Guitars sound nicely fuzzy and pronounced, but you neither have the Grado-in-your-brain-effect nor the K701-detached-boring-yawn-effect. It's just a great crossing of multiple headphones' qualitites to my ears.
I know there's a quite few people who dislike the AD2000 for its somewhat spikey upper midrange coloration, but personally it doesn't bother me the slightest. Quite on the contrary.