A weak battery, although, compared to the OM-D 1, it has a very good one.
The built-in noise reduction is so-so, when the picture is enlarged, artifacts from its work are visible, it is treated by turning it off. It is better to remove it later in the editor, if necessary.
The inability to control shooting through OLYMPUS Capture was frustrating. Sometimes it is required, but rarely, so life does not interfere.
Swivel screen adjustable in one plane only. I would like it sometimes in the other too, but this is not critical and I frankly get to the bottom :)
The lack of a built-in viewfinder and the unrealistic high cost of the native one, which can be purchased separately and inserted into a hot shoe.
No X-sync pin. For me, this is a significant drawback, because. I often use old style off-camera flashes.
The price of various goodies, such as a cable release, viewfinder and other offal, is quite high, but this is solved either by homemade products or by our Asian neighbors - the Chinese. They have everything the same, but three or four times cheaper, and even if something fails, the same cable, it will not be a pity to buy a couple more to replace.