Personnally, I like the form factor very much. The totally retro look, less so. If I hadn't got the E-M5II, I'd be very interested in a Pen with an integrated VF. While I liked the Pens, the optional VF was a nuisance to store. With the Pen F I could put it in a little bag which I like very much and which is too straight for the E-M5II. But one thing would draw me back : from what I have read the VF is smaller than that of the E-M5II. This is a serious disadvantage IMO. I will wait for the serious reviews made with a production camera and see whether the 20MB are producing so much better results than the E-M5. For the moment I have rather decided against it. It is what I have wanted a long time ago, but it is coming too late. Also : I don't expect much improvement from the increased pixels of the sensor; going from 16 up to 20 will make less difference than the upgrade from 12 to 16. Mainly because then the 12MB sensor had a lot of noise.
I am quite in the same boat as you, I owned the EP2 and the EP3 and while I liked these cameras a lot, I never could get friend with the external EVF, so I sold them. And then as soon as the original EM5 became available I bought it and really loved this camera, so much that I then bought the EM1 some 3 years ago and this became my workhorse camera.
I am actually kind of waiting for the EM1mark2 which should be released later this year as I really love the ergonomics of the EM1 and hope they will be similar or better from the new model. But the PenF is also the camera I was waiting for long time, a Pen with integrated EVF. Now as it arrived it even brings a new 20MP sensor, which according to Olympus delivers better high ISO and DR than the old 16MP sensors, but same time with higher resolution. Sure it is a good idea to wait for more reviews, but I will do my own tests as soon as I can get a camera for more time to shoot some RAWs and see how they hold up to my expectations im my main RAW converters - LR6 and C1Pro. But I am confident this will be ok.
Now WRT EVF of the PenF, I know the size of the EM1 EVF, which has the same magnification as in the EM5II and for me the slightly smaller PenF EVF was no problem at all. Especially as the whole camera is smaller and this new EVF employs now finally an OLED display, which is much better than the old LCD display, which is used in the EM1 and EM5II. Better DR, better colors (much more natural) etc.
So I would suggest you go to your dealer of trust and try a PenF personally once available. But I warn you, this test can result in GAS