These new in-ear models from Shure replace (and represent a substantial improvement over) their SE110s, which for all their merits had some overly-prominent faults. Firstly, a complete inability to handle higher volumes (I actually had to set the volume limiter on my iPod). Secondly, a real tendency to distort female vocals - Joanna Newsom's voice sounded appaling (although it's a matter of opinion whether this was down to the headphones) and Adele Bethel (Sons and Daughters) frequently overpowered them completely. Finally, they were simply too 'bright' - they failed to keep control of the high end and the bass was not as well-defined as it ought to have been.
I couldn't be happier to report that these problems have all been solved! The sound retains a similar character to the SE110s, although it is a shade more neutral (thankfully). They continue to provide exceptional sound isolation - even busy roads are kept from intruding on your listening pleasure. They are also comfortable to wear for long periods, thanks to the enclosed 'fit kit'. (As with the SE110s, any complaints that they lack bass is indisputably the fault of the listener not fitting them properly.)
If you keep your music files in high bitrate MP3 or a lossless format (and whyever not, with memory so cheap to come by these days), these headphones will mine them for details like players' fingers on instruments and breathing you didn't even realise were there. It's this attention to detail combined with their outstanding imaging and timing that gives the SE115s their ability to provide a really enjoyable listen. Shure have done a sterling job of tweaking an already very good set of earphones and making them brilliant.
Really, it's a fight between these and Beyerdynamic's DTX-80 for best earphones sub-£100. You will never regret buying either, but I'm backing the Shures. Fight! Fight! Fight! Fight!