I've worked as a music editor for TV, and have worked with some of the biggest ones in film and know them quite well.
In short/in general:
Work-life balance is generally better than composers, but it depends. It can be just as brutal a job in terms of hours as composing (though, the fact that you're probably getting paid a pretty handsome overtime wage makes it easier to swallow), but usually it's for smaller bursts (a few days rather than weeks, or weeks rather than months). Union rules usually make it so that you're managing a day off per week even at the worst of times, though of course even that isn't set in stone. Bottom-line: better work-life balance, but don't expect it to be a walk in the park by any means.
Pressure: less overall compared to composers, but still a lot, which is to say that it's pretty standard for any position in film. Scoremixer's post above is accurate for sure.
Most of the music editors I know share some personality traits that probably attracted them to the work in the first place, and also help them deal with the craziness, when it happens -- they tend to be very laid back, very kind and helpful, and total team players with zero ego. They usually desire a more stable life than that offered by composing, and overall they tend to get it; all but two of the dozen or so that I know were composers who shifted to music editing after getting their early doses of reality working as assistants.
It can be very creatively fulfilling, too. I've actually been itching to do another music editing gig recently...getting the edit juuuust right is so satisfying, especially when you're basically building the cue from scratch from multiple other cues, time-stretching a bunch of stems, adding reverb to stitch some parts together...it's messy and hairy and a very unique gig. However, it requires a lot of "people energy" in that you need to be moral support for both the composer and director, be able to calm tensions when they arise, to deal with composer assistants, all for very little thanks.
Basically, they're the John Paul Jones's of film scoring. If that sounds good to you, it's definitely a career path worth looking into.