Pros: Fun sound, great bass, super-detailed highs. Simply awesome for EDM and rock and metal. Drums and electric guitars really come to life.
Cons: Can be expensive outside of US, need amplifier to sound great. Not really good for portable use.
Really good headphones. I have used them for about ~ 70 hours now and I love them.
If you listen to electronic music, it's hard to find better headphones. Really awesome and fast bass that provides a good punch without messing up the midrange and the rest of the sound. Ultrasone has a kind of special sound, hard to describe, but for me it took a while before I became accustomed to the sound. If you are looking for a balanced and "neutral" sound, you should look elsewhere, since Pro 900 is far from neutral.
I listen mostly to progressive rock / metal where a fast and punchy bass is important, (at least important to me). While they are best for EDM, they do really good with rock and metal as well. I must say that Opeth sound great with them. Never heard the drums this good and the guitars really come to life! Especially in these genres, they are better than my AH-D5000 because of the faster and punchier bass. The midrange is somewhat laid back, but very detailed. This is the Pro 900's biggest drawback for some people if they want a forward-sounding midrange. To me it's no problem at all, I like it. The highs can be somewhat harsh with the wrong source and if you are sensitive. I believe that an amplifier that has a neutral / slightly warmer sound would suit Pro 900 better since they are already pretty "cold" sounding. The soundstage is wide and deep for a closed headphone.
A good amplifier is important. From an iPod they're actually horrible, but with a better amp and DAC they will open up and shine! Quality songs are important as well. MP3 files under 320 kbps or so should be avoided since they really show defects in compressed files.
They are comfortable, but the placement on my head can be a little sensitive because of the S-Logic that Ultrasone uses. It usually takes a while before I get them on and find the "sweet spot". But when they are on, I can wear them for hours. Price is a bit too high in Sweden compared to the States.
Works awesome in games and movies as well. Battlefield 3 sounds really great now!
They are a pair of really fun headphones.