Pros: top quality down and workmanship,ultra-efficient mummy cut and clean, functional design
Cons: reg size (6' length) didn't quite fit me (5'10")
I've used several high quality down sleeping bags from some very reputable manufacturers (The North Face, Marmot), and they have been very good, but they are no match for the WM Apache. I have a long (fits up to 6'6") in the microfiber version from a couple of years ago (the current one in a lighter microfiber weighs 6 oz less), and I can't say enough good things about it. It's hard to believe that they've gotten a 15 deg bag in a size long down to 2 lbs 8 oz (2 lbs 2 oz in the current model). WM's down and workmanship are simply the best, the microfiber shell keeps dampness at bay, and I love the no-nonsense, functional design and the ultra-efficient, narrow mummy cut (some find this confining, but it saves several ounces and also makes it easier to keep the bag warm). I've had the bag for about a year, and I have yet to push its temperature rating to the limit, but judging by how warm it is in the 25-30 deg temperatures in which I've used it, I don't doubt that I could be comfortable in my WM Apache down to at least 15 deg, if not 5 or 10 deg colder.
What finally turned me off to Marmot after nearly 20 yrs of using their Pocket Gopher and Aiguille was the way they started adding all sorts of superfluous features to sleeping bags that once rivaled WM's (Marmot bags are still good, but you pay extra for all that useless flash). In the last few years, Marmot seems to have gone for marketing hype over function. WM, by contrast, has stuck to proven, functional designs while continually raising the quality of the materials used in them. This bag is my favorite piece of gear, and I'll admit to taking it out of the closet and laying it out on the bed more frequently than is normal just to admire it.
My only quibble is with WM's sizing of their narrow cut mummy bags like the Apache (or the Ultralight). I'm 5'10", but I found the Apache in the reg size (supposedly 6') just a hair too short. When I cinched the hood down tight, I found my toes pressing uncomfortably against the foot of the bag. For whatever reason, this was not the case with the slightly roomier, reg size WM Antelope I tried at the same time, but opted against since it seemed too warm for my needs. At any rate, not a big deal, I just got my Apache in the long size, which fits me fine. But I would definitely recommend trying one out in person before you shell out the big bucks.
I was lucky and got mine for $100 off retail when they were closing out the bags made with the old, heavier microfiber. There's no question that WM bags are expensive, but if you use your gear often enough and for long enough, this bag will pay for itself in the long run. I plan to be backpacking for at least another 20 years, and barring theft or backcountry disaster (exploding stoves, down-loving bears), the WM Apache is the last bag I'll own.