The fabric earcups on these guys do breathe better than the P5's leather earcups, though they'll still get your ears a little steamy on warmer days. You get a decent amount of passive noise-cancellation, though over-the-ear models will do an even better job muffling sounds from the outside world.
It's worth noting that the P3s have a straight plug rather than an L-shaped plug. The common wisdom is that L-shaped plugs are preferable. That said, straight plugs tend to offer better compatibility with a wider variety of smartphone cases, which can sometimes leave the headphone jack fairly recessed.
As for performance, the P3s sound very good and like the P5s have detailed, well-balanced sound and good, tight bass. If you're looking for a headphone that really accentuates the low end, this isn't it. These are pleasant-sounding headphones designed to work well with a wide variety of music. They impress on their own, but my view of them changed a bit once I compared them with the step-up P5s. The P5s just sound a bit more detailed, open, and refined. In other words, that extra $100 you pay for the P5s does get you better sound. It's not a huge difference, but it's there.
I also compared these with the Bose OE2i mode that retails for about $30 less. The Bose is more comfortable and has a creamier sound that's rich but not as well defined as the P3's sound. Both CNET contributor Steve Guttenberg and I preferred the P3's sound. I thought the P3 sounded a bit more accurate and made my music sound more present and immediate.
In the end, the P3 is a strikingly designed headphone that sounds very good. I can't say this is a great deal at $200, but it's about what you should expect to pay for a headphone that features this level of industrial design, sound quality, and features. Yes, you can find headphones that sound better in this price range (the Audio-Technica ATH-M50 is one example), but few look as good.
If you're trying to decide between this model and the more expensive P5, that's a tough choice. Because this model is lighter, it's a bit more suited to mobile use, though I have seen plenty of people walking around New York with P5s. Of course at the time I saw them, they didn't didn't have a choice between the P5 and P3. Now that they have the choice, I have a feeling some would opt for the P3. Overall, it may not be as good as the P5, but in certain ways it's better. That's why it's a tough call.