The pants have a close fit, but are meant to be worn as an outer layer, so depending on the temperature, they can be worn on their own (likely over a pair of cycling shorts, as there's no chamois), or over some type of base layer or other tights. They are cut for cycling, so they offer good freedom of movement on the bike, even when combined with another layer. The pants fit closer on the calves and ankles so there shouldn't be any concern about them getting caught in the chain.
The Summit pants are made with a combination of thermal and softshell panels which offer some wind protection and water resistance (but they are not rain pants!), and provide some warmth. On their own, the pants are just right in temps in the upper 30s to low 40s, which is just as Pearl Izumi claims. In the low 30s, I've worn them over a pair of lightweight lycra tights and felt very comfortable. If temperatures dip below that, say, into the 20s, I feel confident that combined with a pair of thermal tights these would still be toasty. One thing worth mentioning is that because they don't fit tight around the ankles, then the ankles or lower legs can be exposed to the cool breezes more than they might with a pair of tights, so I recommend tall socks.
For fit, I have a 32 inch waist, and a slightly longer inseam at 33 inches, and I bought the size medium pants. Fit in the waist for me is perfect. There is no fly, but instead there is wide, flat elastic and shockcord drawstring to fine tune the fit. I am finding them to be pretty comfortable. The length of the pants works for me -- but only just. This is something I've seen with other Pearl Izumi tights in that they'll work for me, but absolutely nothing left to spare. If someone is particularly long-legged, they might find the length lacking. I know there are people who don't want anything bunching at their ankles, but I'll generally prefer to err on the side of having pants (or tights) an inch too long than too short. I'm thinking that PI needs to start offering pants or tights in "regular" and "long."
Like so much cycling-specific clothing today, the price on these is "up there" at about $170. Because of some coupons and specials, I was able to get them for around $135 from my local shop - so I was happy to buy locally.
On the whole, I think the Summit Softshell pants are a nice looking, functional pair of cycling pants that can help comfortably extend the riding season for us commuters.