Ranked in these QuestionsQuestion Ranking
Pro Amazing image stabilization
Pro Great focusing system
The focusing system is quick, it rarely if ever resorts to focus hunting and it's consistently accurate.
Pro In-body stabilization saves money on lenses
Since stabilization can be applied to any lense, you can save money by not having to spend it on stabilized lenses which are generally more expensive than non-stabilized lenses.
Pro Supports standard Four Thirds lenses
Built-in phase detection allows you to use standard Four Thirds lenses via an adaptor.
Pro Convenient in-camera RAW conversion
Pro Quick access to settings
The camera takes a "buttons and dials for everything" approach. It's also possible to change what some of the buttons do.
Pro Great image quality
E-M1 takes sharp 16MP images with tonal colors. There's little noise up until 1250 ISO and there's little smudging up until 6400 ISO.
Pro Good electric viewfinder
The viewfinder is bright and sharp.
Pro Continuous autofocus works well at a distance
Continuous autofocus is reasonably reliable using long lenses at a distance. It works slightly better with the subject coming closer/moving away from the camera than it does when the subject is moving from side to side.
Pro MFT lens mount allows for a wide variety of lenses to choose from
Micro Four Thirds system is a standard used by Panasonic, Olympus, Sigma and many others so you're not locked into a having to buy lenses from one manufacturer.
Pro Can preview HDR images in viewfinder
HDR images can be composited in-camera and the output seen using the viewfinder.
Con Video quality could be better
The video is limited to 24MBit max bitrate.
Con Power switch placement can feel inconvenient
Con Limited framerate options
Shooting in 1080p the camera is limited to 30fps, there are no slow-mo options or 24fps options.
Con Somewhat unintutive RAW conversion interface
Con Continuous autofocus is spotty at close range
Continuous autofocus is sometimes seen hunting with wide angle lenses at short range.