If the Charge 2 is paired with your phone, and you have it with you, I have found it to be as accurate as runkeeper in tracking distance covered. If it unpairs during your run, it is simply back to being a very nice pedometer but is not accurate with distance. While you can set your average stride length for running, it is just an average. If you set this based on running on a flat surface vs. a hilly one you would see a large difference. If you do not set a stride length, I have found it to be way off. Apparently my walking stride is longer than the default, but running is shorter.
As for using it as a calorie counter, I think this is a YMMV situation. I find it fine while friends of mine do not. There was a piece on NPR about how it is most accurate and precise on light skinned, average weight women. I dislike the dynamic prediction of how many calories it thinks I will burn in a day- for example, rather than just assuming I will target 1300 and adding 200 for a run, it will inexplicably think I can now consume 1800 calories/day and this is not true as I would run knowing I will be spending 5 hours on a road trip later in the day and simply need a bit of movement to bring myself up to a normal day's worth of activity.
Like (1) it is reasonably accurate as a pedometer, and if you set the stride length it does give you an accurate and precise distance walked (2) I find the sleep tracking fascinating, and helpful (3) I like the graphical interface, it is easy to read and intuitive.
Disapointment (1) I would like to be able to use it for interval training. I realize I can use a phone app for this, but I can not hear audio cues when my phone is in my pocket [I find it an unnecessary safety hazard to run with headphones], but I can feel the fitbit buzz on my wrist. I'd like it to buzz my wrist for intervals
Dislike (1) Being the master graph-maker I am, I would like to plot data myself for different trend identification. The app has lovely, easy to read graphs, but it will not let you export the data to make those graphs yourself. It will allow you to export day totals & averages. This irritates me to no end.