In one of the least kept secrets in the recent mirrorless market, Olympus finally launched the E-M10 Mark IV camera, bringing that model up to the current 20mp and other Olympus engineering levels.
So what's different? On the outside, virtually nothing other than a IV label on the front. Inside, we get the 20.3mp sensor and an on-sensor IS system that's improved by half a stop (4.5 stops CIPA now). Frame rates bumped up (now 6.3 versus 4.8 with focus). The camera now supports USB charging. The Rear LCD tilts down 180° to a selfie position (compared to 45° before). Plus the camera went on a weight loss program and lost a couple grams.
I've always liked the E-M10. Along with the Fujifilm X-T### and now the Nikon Z50, it's been one of those DSLR-type cameras that are highly competent, have plenty of enthusiast features, but come in a very small and compact package for travel, particularly if you are careful with lens choice.
Sure, you don't get the fabled weather sealing of the E-M1 model and a host of high-end features, but you also don't pay a big price for them (the E-M10 Mark IV sells for US$699 body only, US$799 with the 14-42mm f/3.5-5.6 kit lens; US buyers before November 1st get a bag, an extra battery, and a 32GB SD card, too).
My primary problem with the E-M10 is now the focus system. Still no phase detect. This is probably the most limiting feature of the model, and one you need to be aware of.
One other problem: the Panasonic G100/G110. The Panasonic is a bit smaller and lighter, but definitely in the same class as the new E-M10. The Panasonic has a slightly better EVF and Rear LCD, a better orientation for video (swivel LCD), but is missing on-sensor IS.
This competing twin is both good and bad news.
The good news is that clear competition like this means you now have some clear choice in the market, if what you want is a very compact m4/3 DSLR-style camera. The bad news is that I don't think there's enough demand at this position to justify two competing cameras.
Indeed, this is about the closest Olympus and Panasonic have ever come to producing similar products in the m4/3 space after a decade of mostly making different decisions and creating more variety in choice for customers. A GH is not at all like an E-M1 in many, many ways, and that same difference of product targeting has created a really wide range of choices for customers who want an m4/3 camera.