As always, Arc'teryx never fails to deliver (I think I'm a little biased to Arc'teryx products at this point). I've only been able to use these pants a few times now and they have been amazing. I love the full side zips, it makes getting them on so easy. I threw these on when it started raining on a winter route and I didn't have to worry about my crampons tearing a hole into my expensive pants. The full zip design is simply the best when it comes to mountaineering hardshell pants. The boot hooks and hem cinch are awesome. I didn't even use gaiters when hiking through the snow; its that good. Also, they're totally waterproof (it is Goretex) with a great DWR coating to bead off the water.
These pants are made from gore paclite, but the face fabric is plenty burly. The paclite makes them super light weight so I have used these pants just as rain pants as well. They breathe very well but I wouldn't want the inner fabric in direct contact with my skin. Be sure to wear long-underwear under the pants if you use them as rain pants.
As a reference, I'm 6' with a 32" inseam and very skinny. The small actually fit great and gives me enough length in the legs. I think the sizing guide is off on all Arc'teryx hardhsell pants though... they seem to run a little longer than suggested by their size charts.
Overall: great, versatile pants that can be used all 4 seasons!