When choosing between my DSLR (Canon T4i) or GM1, the GM1 usually win out purely for convenience. After using the Olympus M.Zuiko 25mm f/1.8 the GM1 has completely closed the image quality gap as well.
I don’t know enough about lens and camera jargon to call this a “review”, so I’ll just share my subjective impressions. On the DSLR side I’ve used the Canon 50mm f/1.8 II, Canon 1.8 f/1.4, Canon EF-S 18-135mm f/3.5-5.6 IS, Canon EF-S 55-250mm f/4.0-5.6 IS II, and Sigma 18-35mm f/1.8 DC HSM. In terms of color, sharpness, and focusing, the Olympus outperforms all of those lenses save for the Sigma. The Sigma is double the price, and significantly larger and heavier, and to me the performance advantage isn’t worth those tradeoffs. DxO hasn’t tested the Olympus 25mm, yet, but they have tested its nearly-identical older brother, the 45mm 1.8.
I preface all that to say that the Oly 25mm 1.8 is a really great lens, and combined with the GM1 you get stellar performance in a small package. I’ve been shooting micro four thirds for 9 months now, this is the first lens that’s made me truly buy in. Focusing is accurate and lightning quick, it produces super sharp images across the frame, and manual focusing is smooth. I really don’t have too many negative things to say about the lens. It feels nice in hand, it does slightly throw off the weight balance of the GM1, but one handed use is still possible (though not ideal). But enough of the talk, here are sample images straight from the camera, no editing at all.
f/1.8, iso 1600
f/7.1, iso 125
f/1.8, iso 125
f/1.8, iso 400
f/1.8, iso 500
f/1.8, iso 200
As you can see from the range of images, the 25mm focal length on MFT makes for a great walking around lens. Its wide enough for landscape compositions, and you can get close enough to capture individual subjects. And the bokeh! You can really capture some dreamy bokeh with the Oly 25mm.
Those are my thoughts on the GM1 and Olympus 25mm f/1.8. If you have any other questions feel free to ask.
Adam J. Reid 
March 30, 2017 at 8:08 pm
Hi Adam, it’s been almost a year since you last posted anything here, and a few years since you posted this particular review but I hope you still get comment notifications! Anyway, I’ve a question about the *silver* Panasonic GM1: do the silver tones in the Pany camera and Olympus lens match nicely? Bit of a silly question but still, I’m pondering an (online) lens purchase and would like to know this. Thanks!
April 3, 2017 at 7:14 am
Hi There! Unfortunately the silver tones are pretty different. The Oly silver is darker and more metallic/shiny, whereas the Pana is lighter and more matte. The difference doesn’t bother me much though, the 25 stays on my gm1 to this day!
April 3, 2017 at 2:05 pm
Thanks! That’s not a problem. I’m also getting a silver 15mm Leica too. It probably matches the body.