The Miura 20 is a solid, versatile, built for hard use and easy on the eyes backpack. I also own the discontinued RT25 and I have put that bag through the gauntlet. I bought the M20 to serve as a replacement, if only because my RT looks a little rugged (though I still use it to full capacity). And while it's not exactly a 'next gen' RT, it is obviously from the same train of thought.
pro; If you have an Arc'teryx backpack then you know the quality of make and unique styling. Roll top is crucial. (why don't you see more of these?) Both outside pockets are Tardis-like, open the zipper and the cramming space is vast. The jury is still out on the metal accessory-strap-fastener things but they will never break. Gone is the molded foam back in favor of more breathable fabric combination and in fact a more contoured shape. Main pocket is substantial enough for a weekends worth of clothes and cameras and books and so on, and is lined for hang up free packing.
con; Those two zippers on the sides (completely opening the main compartment) are cool, and burly, but just not necessary. One of the things I really like about the RT is that it's a big sack. Those two zippers really just increase the likelihood that you'll accidentally yard sale your gear in the airport or bar (keep 'em buttoned!) And there's another, even more useless zipper on the inside of the main compartment accessing the vertical outside pocket, but not a two way zipper. Inside going out. huh? I have absolutely no idea what it's for. Really, I'm baffled.
In summation, if you're looking for your next RT the M20 is kind of that. Though, where the RT looked a little foot-soldier-of-the-future, the M20 is totally bring-your-yoga-clothes-to-the-office or best-dressed-at-the-weekend-war.

I cannot say enough for the quality of this pack, absolutely great construction with great quality nylon and zippers. The length is a bit short for my build but not so bad once you get used to adjusting it. It really is deceiving how much it holds, truly 10 lbs of S*** in a 5 lb bag with this one. on a recent business trip I and my associate had similar gear to pack and his bag was twice as large as mine to fit it all. easily fit my laptop, Leather folder, Arc'teryx covert hoody, Arc'teryx Theta SL shell, my 80gb Zune in a pelican 1020 microcase, Sony PSP, Blackberry, Sunglasses in a case, extra pair of socks, and all my boarding information. It was pretty full at that time but not anywhere close to pushing the seams.

Pros:
-Roll top is a great feature and the side zippers that run the length of the pack make packing a breeze
-adjustable and movable gear straps on the outside are great for holding a sweatshirt on weekend travels as well as a coil of rope when they are moved to the top of the pack
-internal frame is a refreshing feature on such a small pack and what led me to purchase
-fits fantastic in overhead bin on an airplane
-Yellow interior reflects off of a headlamp so items at the bottom can be found super easily in the dark

Cons:
-Pack is very short and takes some doing to find the right adjustments to make it work (I am 6ft tall at 200lbs with muscular build)
-shoulder adjustment straps are a nice idea but with a pack so small they don't offer a whole lot of use
-Made in Philippines

Overall I recommend this pack for its superb quality and good use of fabrics and strapping, but keep in mind if you have a larger build you may be disappointed.

I am surprised that Arcteryx could miss so badly. This pack is way too short and it sits very high on the back. The straps are also too close so the pack does not hug the back properly. The roll closure with the zippers is a neat idea, but the extra hardwear kind of gets in the way and the roll closure does not work as well as it used to work on the older RT series packs. Overall, a step backwards for Arcteryx.