I wrote this up for Andy, so I might as well post it here too...sorry for the length:
The LCD2 is a very nice headphone. I don't consider it the king of the world the way it's being hyped up right now, but it is definitely a great deal at under $1000. It has a very similar frequency response to the O2mk1 to my ears. I think the O2 is better at pretty much everything though. The O2, and electrostats in general, are a touch faster, have a little more clarity, and are more detailed. For instance, the O2 and Lambda Signature are very good at letting you hear the room during a recording - the LCD2 not so much. That very slight delay in very low level echo when sound is recorded in a room is pretty much lost in the LCD2 (and most headphones). This can make the LCD2 sound more intimate and personal, but I prefer to have that detail as it sounds more alive and real. This is most noticeable with live recordings, where the LCD2 can at times make a live album sound like a studio album with an audience thrown in. I'm not sure you can picture what I'm talking about but it's something I noticed. To my ears electrostats are also much superior to dynamics at revealing pitch and allowing you to focus on any instrument you want at any time without trouble (especially when playing midrange notes and bass notes simultaneously). I don't know what causes this, but I think it might be due to there being "less impact" and lower distortion in general. The common comparison used to explain this is the way a large car subwoofer will produce bass but all the bass notes sound very similar, whereas listening on an electrostat takes it to the other extreme by presenting you with the pitch and texture of every bass note. I'd say the biggest difference in frequency response between the O2mk1 and LCD2 is in the upper mids and highs. The LCD2 has more presence in the upper mids/lower treble area and this results in a slightly bigger emphasis on the sound spectrum commonly mistakenly referred to as "detail" - things like tape hiss, sibilance, bad recording artifacts, and the small time sometimes captured when a finger initially hits a metal guitar string are all more prominent on the LCD2. This in turn gives the O2 a slightly smoother sound that can make even bad recordings sound nice, whereas the LCD2 is a little less forgiving. From the mid treble to upper treble, the O2 has a little more presence than the LCD2, which is pretty much air. This is explained earlier - part of what gives you the sense of area of a recording space. The O2 is also better at imaging, but that's one of the many things it does best. Another difference between the two headphones is that the LCD2 has a thicker sound. The O2 has a thick sound compared to other electrostats, but the LCD2 probably has the most impact throughout the audible frequency spectrum of any headphone I've heard. I can see somebody having a preference for either presentation.
I know all of the above probably makes the LCD2 sound horrible, but it is actually a great headphone. I am being pretty nitpicky, and this is compared to a very high caliber headphone. In comparison to most other headphones, the LCD2 is great at everything. If impact, a natural sounding frequency response, tonality, imaging, and extension are high on your list, this is a definite headphone to look at. This is pretty much all I have to say on the LCD2 as I'm not really one to attempt full blown reviews and try to only report what I'm fairly certain I hear instead of what I think I hear.