I use Canon cameras at work - a mix of 5D Mark II and 1D Mark IV bodies - but I don't really want to haul those things for personal use or on the trail. So over the years I tried all sorts of "high end" compacts with mixed (but usually poor) results.
Now we're pretty invested in the Micro 4/3 system. I bought a GF1 three years ago, with the 20/1.7, and it was a revelation. We followed that with a G1 and a couple of zooms for my wife, then a GH2 for me, and recently a G5 for her, along with several good primes and now the Panasonic 12-35/2.8 zoom (which is a 24-70/2.8 equivalent with IS. Pretty sweet.) Still trying to find cash for the 7-14/4 and the Olympus 75/1.8. Also, we'll need another 12-35/2.8 since my lovely wife used it once then spot-welded it to her G5 ;-) Don't think I'm getting it back.
We use these for personal work, travel, and sometimes I use one as a carry-around camera at work.
Image quality: good, but not as good as the big Canon cameras of course. The GH2 and the G5 are very similar, with decent results at ISO 3200. I shoot a lot of indoor low-light photos of friends at local music nights, and the files are good (shooting raw and processing in Lightroom.) The Olympus OM-D is a big step up in image quality (and I'd like to find the cash for a pair of those to replace my current cameras.) See the Thom Hogan review for example. (http://www.sansmirror.com/cameras/a-note-about-camera-reviews/olympus-camera-reviews/olympus-om-d-e-m5-review.html)
Depth of field: of course the shorter focal length provides less control over shallow DOF. The fast primes help, and in some ways it works better than using a full frame camera -- shooting at f/1.7 with the 20mm, or f/1.8 with the 45mm, provides just the right amount of in focus area for a portrait -- more than the "one eyelash in sharp focus" that I get with the 85/1.2 on the Canon -- but with the creamy smooth out of focus areas that I want behind the subject.
Lenses: the best selection for compact interchangeable lens cameras, period. Zooms ranging from kit lenses to mid-range to professional quality - that Panny 12-35 doesn't feel, handle, or shoot any worse than my new Canon 24-70/2.8, and the Panny has IS which the Canon does not. Excellent choices in primes, too, from the Sigma f/2.8 primes that run $200 each, to the mid range Panny 14/2.5 and 20/1.7 and the Olympus 45/1.8, to the excellent Oly 12/2, 17/1.8, 75/1.8, and the Pana/Leica 25/1.4. Panny has announced a 150/2.8 to arrive next year.
All of these cameras and lenses are less than half the size and weight of my Canon gear. This, to me, is the best part -- I can carry a small Domke bag with 2 bodies and 4-6 lenses, and barely feel the weight on my shoulder, but still get the photos that I want.
Recommendation: the Olympus OM-D EM-5 and the Oly 17/1.8, or the Panny 20/1.7. This provides a (FF) 35mm or 40mm equivalent FOV in a very light, compact, fast package with excellent image quality.
My daydream right now is to have a pair of OM-D bodies and the appropriate lenses and use them at work -- I can easily cover 80% of my assignments with that kit, and I'm getting to the point where humping big cameras all day is getting awfully old.
Oh, yeah, and to relate this to backpacking: I carry either the GF1 with the 20, or the GH2 with the 12-35 for a trail camera, depending on the situation. Light, compact, easy to carry, not UL but so what. Tried carrying the 5D Mark II and the 24-105 on a weekend hike last summer - ugh. Big difference with the small cameras.