My sole complaint about the interface is that some of the buttons are flush with the body and hard not only to feel, but to press. This includes the movie record button, which provides little tactile feedback and the Q Menu button, which is simply too important to be so hard to feel. The silver buttons are also etched, rather than labeled, and it's nearly impossible to see the etching in dim light without tilting the camera toward a light source.
My biggest design reservations have nothing to do with the camera and more to do with the X series lens, and the lens in kit with the camera. I really like the concept behind the powered lens, and that it automatically retracts when you power off and becomes quite compact. It's quick and quiet, with good stabilization, and optically seems about the same as its traditional 14-42mm counterpart.
But the placement of the zoom and manual focus switches is really awkward, especially if you're shooting without the optional EVF; I always feel like I'm contorting my hand to operate the zoom when holding the LCD at eye level. My thumb naturally falls on the manual focus switch, which left me frustratingly trying to zoom while accidentally operating the wrong control. Furthermore, using a switch for manual focus feels annoyingly imprecise compared with a manual focus ring. The lens is really optimized for shooting video, and the location of the switches seems like it would be most comfortable either with an EVF or articulated LCD, neither of which the GX1 has. Given how much extra the lens costs over the older kit lens, I highly suggest trying the camera with both before buying.
The feature set is solid, but there's nothing particularly exceptional beyond what competitors offer, and a tilting or articulated LCD would be really nice. It does offer a seven-shot exposure bracket, with a six-stop range, which should appeal to HDR shooters. Panasonic introduced a new AF mode with the GX1, AFF (Autofocus Flexible), that's designed to adjust to small movements of the subject that presumably fall through the cracks between tracking AF and continuous AF, but I couldn't get it to exhibit any advantage over the older AF methods and focus area options--and for which the GX1 offers a lot of choices.
The GX1 may not have retro-tastic looks, but it's a well-designed, really good ILC that's got a lot to offer advanced shooters, as long as you're not trying to capture sports. Definitely try out the power zoom lens before committing to that kit, though.
(Shorter bars indicate better performance)
(Longer bars indicate better performance)