DxOmark tested the Olympus 25mm f/1.2 PRO lens and the conclusion is:
At $1199, the Olympus 25mm f/1.2 is not cheap, but you get a lot of lens for your money, with weather-sealed barrel construction, advanced optical construction, and a super-wide f/1.2 maximum aperture. Its excellent light transmission ranks it as one of the highest-scoring MFT-mount lenses we’ve tested on the E-M1 II, only fractionally behind the Panasonic 25mm f/1.4. It achieves a slightly higher overall sharpness score compared to the Panasonic alternative, however, and significantly less geometric distortion, which could be important if you want straight lines not requiring correction in post-production. Performance at the maximum f/1.2 aperture is good, but closing down to f/2 notably improves center resolution and reduces vignetting. For peak performance, consider shooting at f/4 or f/5.6 on the Olympus 25mm f/1.2.