The best it's own specific class

I love these headphones. I bought them as an upgrade to Grado SR-60s, initially because I needed isolation (sound blocking) but I quickly fell in love with the sound.
These are not "sparkly" sounding headphones. They don't sound dead either, but they're definitely on accurate side of things.

The bass is excellent. If you haven't ever really paid much attention so your audio equipment you might still have noticed, with the sort of things put out by the big manufacturers, that the bass response is somehow... frustrating, on your Sony's, JVC's, etc.
These headphones are the solution. The response is controlled, somewhat raised in the mix, but very tonal and not at all boomy. This makes these headphones especially good for music where a driving bassline is important, but benefits all music.

Some people say these have "rolled off" highs, meaning the higher frequencies are toned down in the equalization. This is probably true, however it is not really a flaw for me, and likely wouldn't be for many people. First of all, it's not a truly severe imbalance in the sound, it's pretty subtle. Also, the highs are very detailed and clear, they're just a bit quiet. In my case, I am extremely sensitive to high frequencies and they hurt my ears after a short time. These headphones, however, I can listen to for hours with no problem.

These are 80ohm headphones. I've found that they do sound best from a more powerfull source like a home stereo or component CD played, but they sound acceptable out of even a wimpy Sony discman. The main loss on low power sources will be the "confidence" of the sound, and the bass will lose some impact.
You don't really need a dedicated headphone amp for these though. Even the audio out on a soundcard drives these 80% of the way to perfect, I'd guess.

The noise blocking is good but not exceptional for a closed headphone. I've found the Sennheiser HD280 has better noise blocking, along with Sony "dj phones", but really, neither of those compare sound wise with this.

Part of the reason this doesn't block quite as much noise, I think, is the fact that the earcups are velvet instead of pleather. A worthy trade in my opinion, these are extremely comfortable headphones. Another plus is that they're not that big, and they don't stick out much, so you won't look silly wearing them around. (NOTE: those with really big ears are advised to try before buying- they might not fit right)

They're also a simple black design without any tasteless plastic moulding or visual gimmicks. I with more manufacturers could have the intelligence to use this sort of elegant design. One thing: They do not fold, you can't compress them down into a suitcase. Fortunately, they aren't too big either, so it's manageable.

Speaking of the constuction of the headphones.. It is definitely tough. I carried these around in my backpack for weeks at college. They're made of a tougher plastic than you see in most products. Best of all, the headphone is designed to be disassembled and parts can be replaced, so when you wear out the earcups, or the headband, or the cord, you can get them replaced.

The cord is coiled, like a telephone receiver. Some people don't like this, but I think it's great. For one thing, if you forget you have them on, and start walking away from your stereo, they won't suddenly snap your head back like other headphones. You'll notice a gradual tension as the coil stretches. Also, the coil reduces tangles. The connector is a gold plated miniplug with a 1/4 adaptor that can securely screw onto it. Solid.

These are the best headphones for a specific class: If you need headphones that block outside noise, will work without an amp well, and you don't like putting things inside your ears, these are the best option. There are higher sound rated open-type headphones at this pricepoint, and supposedly the BEST noise cancelling system sound wise is the Etymotic earbuds- but the DT250-80 is unrivaled at doing what it does.

You pay a lot for these headphones, but they're worth it. Unless you're really brutal, they won't break. Even if they did, they could be fixed again. They have a sound that is great for the long run for most types of music. You won't get tired of that. For me, these may be the last headphones I need to buy.