Pros
Great prodeals on gear. I got a $575 North Face hard shell for $95 through a special North Face was offering to REI employees. Work-life balance - they are great about giving time off, as long as you give enough notice (3 weeks). Otherwise, it is up to you to find your replacement. I've had some managers who have been really great, and some, not so much. It all depends on the managers who are at your location.
Cons
They promote management that doesn't always have the skills to communicate effectively, whih in turn can negatively effect the whole store. The pay is low compared to retail industry standards. It really is only a place you want to work for discounts and spending money. They only hire part-time. Hours can be incredibly difficult to come by during the slower times of the year. Too much focus on membership sales. People who sell a lot of memberships but know little about gear get rewarded with hours.