This is by far my favorite small pack that camelbak offers. It is large enough that if you want to you can use it for a day trip (although its really tight and its hard to fit a jacket in it along with other supplies and food).
I own 6 camelbaks and I use this one the most because it is good for almost anything besides a big day trip or anything longer than a day. This is the second one of these that I have bought, I gave the first to my best friend after buying this years version of it.
I love the organization pockets and exterior pockets and the rain jacket is awesome. The built in rain jacket is such a plus because you can get away with not having a rain jacket on warm summer days (the important electronics and supplies will be kept dry inside your bag).
Not all M.U.L.E.s have a built in rain jacket. Only the M.U.L.E. NV has one, not the standard version.