I'm afraid it looks bad. Do you need the small cabinet on the left? I think it would look better without it. Then the space would not look like a mistake. You could put a clock in the area between the window and the other cabinet if you feel you need to fill up the empty space.

Matching open shelf for spices or other kitchen accessories.

I agree with the shallow open shelf idea. It would fill the space and look like it was intentional.

Island Grove Estate Kitchen · More Info

On the right you have a corner cabinet which comes in only one size, so you left with whatever space you have left. If you match the reveal on both sides to make it equal, left side cabinet would be very narrow. The only way to make that work, instead of the corner cabinet there should have been a blind cabinet.

I would say remove the cabinet on the left and put open shelves there leaving the same spacing where the shelves end as where the right cabinet ends. The matching glass doors don't match exact because one is at an angle. I would only attempt to put a narrow shelf on the right to balance the current left cabinet if you have at least 5" to make the shelf useful.

I think adding small/narrow shelves is a good idea (as are the other suggestions already given). If the shelves were glass, they would provide some balance without being overwhelming or conspicuous.