There are a number of comparisons that would seem to be appropriate for the Panasonic Lumix DMC GH3. Some demonstrate how good the camera is and others are not be quite so favorable.
One particularly interesting aspect of establishing an appropriate comparison is the absence of either Canon or Nikon. Neither the Canon EOS M nor any of the Nikon 1 range score as high and while cheaper than the Lumix there are better alternatives. In the Hybrid sector Sony stands out. The top Hybrid: Sony’s NEX-7 has a DxO Mark score 10 points ahead at 81. Three other Sony models also beat the Lumix, the NEX-6, NEX-5N and NEX-C3. The NEX-7 is much more expensive and has a 24MPix sensor but the NEX-6 has specs similar to the Lumix, though with a physically larger sensor and it beats the Lumix in all measures: 78 overall, a full bit of color depth, 2/3 EV in dynamic range and about 1/3 EV in low light.
Taken as a part of the Panasonic range the Lumix DMC-GH3 is the newest and highest priced. It is much better than the previous model: the Lumix DMC GH2 which had a DxO Mark Score of 60. The GH2 was quite a disappointment, it scored lower than the 12Mpix, Lumix DMC GH1 which had an overall DxO Mark score of 64 and was launched back in early 2009. The GH2 remains the second best of Panasonic’s Hybrid cameras.
As a member of the broad range of hybrid cameras that includes APS-C cameras and ones with sensors smaller than 4:3 the Panasonic is joint 7th. The group is dominated by Sony NEX cameras: 6 of the top 10 coming from Sony, but what stands out is that while the Lumix is the second most expensive hybrid camera, it is eclipsed by the Pentax K 01 which is only 2/3rds the price and has a DxO Mark score of 79.
An Alternative way of looking at this would be to ask what you could get with the same budget? Cameras with an indicative price between $1000 and $1500 include some very good kit, top of the rankings here being the Pentax K-5 IIs which has a DxO Mark score of 82 and sells for nearly 10% less.
The brand that scores equal to, or higher than the Lumix, but has the same lens mount – Micro 4:3 – is Olympus with the PEN E-PM2 at DxO Mark score of 72 and the OM-D E-M5 which scores 71. They have virtually the same color depth, fractionally lower Dynamic Range and fractionally higher low light performance. If you read through the other specifications they match one another almost point for point except that the Olympus PEN E-PM2 has no viewfinder and the screen is fixed, without tilt, though the OM-D E-M5 does. Both the Olympus cameras are cheaper, the PEN E-PM2 is nearly half the price, so the viewfinder may be a sacrifice worth making for a photographer looking for a really compact system camera. It is worth noting however that the measurements for both the Olympus cameras did show significant variance between the measured ISO and the Olympus’s stated ISO, around a full EV, since it appears to be consistent it is something that you could easily work around but it is there nevertheless.