Firstly, I'd like to say the sound isolation is very good. It feels like putting on a pair of earplugs! The Shure ear buds expand in your ear and almost enlarge them. You get that amazing noise isolation, but it's sometimes weird to feel my ear canal getting noticeably larger.
Secondly, the build quality is solid. The cables are detachable and feel strong though a little bulky. Some may find the over-the-ear style quite weird, but I think the cables are 'less in the way' and I like the hearing-aid look. One thing I don't like is the cable length of 1.65m long - it's almost as tall as me.
Finally, I feel that the SE425s has a distinct sound signature. It's a different character to headphones I've used in the past which have had more powerful bass. That's not to say the SE425s lack bass, but it is less prominent, more 'tight' and does not over power the mids and highs. As a result, there is a lot more clarity and differentiation can heard between various instruments, voices etc. Lossless tracks sound sublime.
Overall, a quality pair of earphones with a distinct sound. They will last a long time.