I'm a huge metal fan here. It's almost all I listen to. The phones I have are the DT990 and Ultrasone HFI-700, but I have also tried the HD650, HD280 Pro, Grado SR60, and Grado SR225. I find that people seem to like Grados for metal, and I can see why. They have a great sound for guitars that's really crunchy and fast, but I don't like their bass. Perhaps it has something to do with open headphones, but I just don't seem to be a fan of the way their bass sounds. Let me elaborate.
The first headphone I got when I started exploring hi-fi over a year ago was the DT990. I really liked how it sounded, but the bass was unsatisfying. Everyone on head-fi will tell you that the DT990 is a bass monster, but I don't feel the same way. At fist, I just though I must be a huge bass head, but I definitely don't think that's true anymore. You see, what I really just wanted and what, I think, is so important to metal is bass impact. You can probably tell by the name that it means the slam you get from a kick drum, or just the feeling you get of being punched in the chest by a powerful sub in a good speaker system. If you like metal, then you know what I mean.
If impact sounds like something you want a lot of, then the only headphone from my experience that I can recommend it the HFI-700. I'm listening to Godflesh on it right now. It has by far the best impact of the headphones I have tried. Also, the bass extends VERY deep. The problem I have with my DT990 is that, although there is a lot of bass, it mostly sits around the upper low end and lower midrange. The HFI-700 is a pretty balanced sounding headphone, which is why I was so shocked to hear how much bass it had (especially impact). The bass is pretty uniform across the spectrum, so raising volume does not make the mass in the upper low end and lower midrange overpower other frequencies, but it does bring out the phenomenal impact and bass extension.
My one problem with the Grados was their pretty anemic bass. They (SR225 and SR60) just could not get down low enough to hit those extra low notes that often come up in the music I like. For example, at the beginning of "Love?" by Strapping Young Lad, there is a very low explosive sound. Listening to this song on the Grados (or any of the other phones I listed, except the senns, which I have not had enough time with) was sort of like watching the low end happen, but not feeling it. I could tell the note was there and I knew that if I were listening to it on a nice speaker setup, I would be able to really feel it hit. The impact on the SR225 was decent, but nothing to write home about. It was definitely much stronger in highs and mids.
Okay, that was a really long post, so I'll wrap it up already. Just know what you like from your sound. If you want very good guitar sound and are willing to sacrifice bass for it, Grados are a very good choice. When I heard the HD650, it had some nice impact and sounded pretty good otherwise, but I only had a few minutes with them and, therefore, cannot tell you enough about them. I would not recommend you get the DT990s for metal, although I love them for other things (gaming sometimes) and they are soooooo comfy! You can probably guess that the HFI-700 is my favorite headphone right now, so obviously that's the one I will recommend. If you like impact and speaker-like bass extension as much as I do, then go for it!
