I say "true SLRs" because, technically, the DMC-G1 isn't one. It has no mirror (the "reflex" in "single-lens reflex") and no mechanism to reflect the image captured by the lens through a prism and then to an eye-level viewfinder. Instead, it relies on a 3-inch wide-screen LCD and an electronic eye-level viewfinder.
Though you do get a live view of your subject through either the LCD or the viewfinder, you're always looking at pixels, rather than an image reflected through glass. As good as the eye-level viewfinder is for its type, I disliked using it, especially in full sunlight, because I found it hard to see while I was squinting. At least the DMC-G1's LCD refreshes at 60 frames per second instead of the more standard 30 fps, so in better lighting it gives you a really good view of your subject.
The DMC-G1's design uses a smaller sensor than most SLRs do, which allows for a more compact camera body and smaller lenses. This model is noticeably lighter than other SLRs, but it's still quite bulky: It's more like the size of the models on our , which rates cameras that have manual exposure settings but aren't SLRs. And I found that the DMC-G1 is only about a quarter-inch shorter and just a half-inch thinner than the digital SLR I used for comparison (when both cameras had lenses attached). I had trouble stowing either camera in tight spots, and I certainly wouldn't take either one to a dinner party, for example. Nevertheless, the G1's lighter weight and smaller size make it easier to hold at awkward angles than most SLRs.
The camera comes with a 14mm-45mm lens, which provides the same as a 28mm-90mm focal length in 35mm-equivalent terms. Micro Four Thirds is a new design from the same companies that back the Four Thirds system (including Fujifilm, Kodak, Olympus, Panasonic, and Sigma).
At this time, the only other available lens is a 45mm-200mm lens, which goes for US$350. If you purchase a $170 adapter, you can use Four Thirds lenses (note the lack of "Micro"). The Micro Four Thirds lenses do have true, seven-blade diaphragms, so they should function as any SLR lens does; however, because they are significantly smaller, they have much less glass, and that should have an effect on their ability to bring in light. The lens aperture on the kit lens is f/3.5 at its widest setting and f/5.6 at its longest setting; those are typical ratings for low-end SLRs, but the lens still isn't very flexible.
In our tests, the DMC-G1 made a less-than-impressive showing. Test images looked dark, and the white balance--at least, when we used its automatic white-balance setting--was really off on a couple of shots. However, one of our test shots requires manual settings, and on that test the DMC-G1 performed much better (most cameras do). Its shots weren't extremely sharp, compared with competing SLRs. Its battery held out for 437 shots--not bad, but most SLRs reach (and surpass) our 500-shot test limit with ease.
The DMC-G1 has extensive exposure controls, of course--aperture- and shutter-priority as well as full manual--but it also has some more consumer-friendly controls, such as face detection, four scene modes, and a few interesting options under the standard shooting modes (for example, in Portrait mode, you can choose from Soft Skin, Outdoor, Indoor, and Creative).
A button on the top-right corner of the camera labeled Film Mode lets you choose dynamic, nature, smooth, nostalgic, vibrant, standard black and white, dynamic black and white, or smooth black and white. It allows for exposure bracketing and white-balance bracketing, but no focus bracketing or flash bracketing. It does have a very useful focus-tracking function: Just aim at your (moving) subject and press and release the shutter, and the camera will lock on to the subject as long as it remains in the viewfinder. When you see the shot you want, simply press the shutter again to take it. The camera lacks video-capture capability, as you'd find on point-and-shoot and advanced cameras (the Nikon D90 is the first DSLR to offer video capture).
I'm sure that the compromise that gives the DMC-G1 its smaller size and lower weight, at the expense of some capabilities, will be okay with some people, but considering the $800 price tag, I'm not impressed. For that kind of money, I could get a pretty darn good true SLR--for example, a , a , or a . Though the Panasonic Lumix DMC-G1 mimics an SLR in many ways, it strikes me as more comparable to a camera like , albeit one with interchangeable lenses. Furthermore, the lack of available lenses (for now) makes the distinction between those two models smaller than you might imagine.