They're closed, but not super-isolating, a good tradeoff between not leaking sound, and being able to hear my phone ring.
They're very comfortable, more so than other phones I own (At home I have a couple different pairs of Grados, Beyers, and AKG 301s).
They also drive well of a standard headphone output, when many audiophile grade phones (the AKGs and most higher-end Sennheisers, for intance), don't.
Other than that (and the headband cracking) those are one of the best headphones I've ever had.
BUT, they were poorly tested. Both sides have broken where they slide out of the headpiece to extend.
Spent $5 at home depot and with a bit of drilling they are now reinforced and back together.
For monitor use, and by that term I'm talking about actual pro-audio where isolation is a plus, really the high end custom IEM (IEM = in ear monitor) is where it's at.
But as with most things, be careful what you wish for. A true reference can be boring unless you're using well mastered source material. Most pop/rock/electronica doesn't fall into that category, and with that notion it's best to listen to a bunch of cans and let your ears be your guide.
The components in my chain cater to my preferences. It's not the most uber-accurate, but for my purposes emotional engagement is key - it let's me tune out from my environment and focus on my work.
I've moved considerably upmarket over the years and won't talk about the rest of my setup, but my main cans now are Ultrasone Editions 8s. They're very pricey (retail $1500 for the basic model, but you can get them used under $1k if you spend enough time on the Head-fi classifieds). They're considered by many to be the best sounding _closed_ cans out there, and they actually isolate almost as well as good iems. Plus they're very light and comfortable at 260 grams.
So yeah, that's quite a bit of money and I am certainly an audiophile. OTOH, I use them an average of 4 hours a day and bought them used, so when the time comes I can sell them at little to no loss. I get a great deal of enjoyment out of my rig and it helps me to do my work, so I consider it a good investment. Same with my Knoll Life Chair. YMMV. I actually made a profit on limited edition headphones in the past, purchased a used pair of Audio-Technica L3000s for $1500 in 2005, sold them for $2000 in 2007. Today they tend to go in the $2500 range.