I picked up an F4 cheap as a stop-gap after killing an F3 in the fall. F3 prices were really high, F4 prices really low, I was curious....
The F4 definitely doesn't have the hipster, film-camera look of an F3 or FM/FE series camera. It's bulkier, chunky in a strangely-streamlined 80's way. My girlfriend remarked straight away that my previous film camera was cooler. I wasn't too put off by the size, my F3 usually goes with the drive mounted, but I wasn't sure I'd keep it.
So, I took it out and started shooting. It's probably the best-handling SHOOTER I've ever had. Sure, the F3 is close (as are, IMHO, the single-digit D-series and the D700/800 line, if I'm allowed to say so here), but the viewfinder is big and bright, the mirror is VERY well damped (the F3 feels much harsher and clunkier after spending time on an F4), you gain a useful flash synch, still have access to a full lineup of good screens....
Basically, if all you're doing is shooting it, the F4 is a way better choice. That said, for a travel camera or EDC an F3 with a few small primes is noticeably lighter. So if I'm going out expressly to shoot and it's in a situation where being inconspicuous isn't necessary I'll pack the F4. I just think that isn't what most people are doing with 35mm cameras these days, a lot of them are either posing (carrying a camera as a fashion accessory), doing street photography, or documenting their lives and travels. Those aren't situations where a massive hunk of gear is the best choice.
For me it's been great, I recently did some wildlife work using it and found the focus confirmation very helpful. The matrix metering also helps with nailing the exposure on slides. I am also planning to bag it along with my non-film bodies for some upcoming work, in case the opportunity to bag a few more artistic/personal work photos comes up.
At the end of the day, though, what another forum member said about the 180 2.8 comes to mind, the gist of their comment - "Only a nikon shooter could love it. It's big and heavy and a good piece of glass".
Same applies to the F4. You have to like an overbuilt piece of gear that'll break your back in your bag but get out of the way and JUST WORK when it's in hand. It is also a bit niche, being a very primitive AF camera (though far from the worst I've used) and a very advanced, very large, MF camera. To each their own, but I hope we can keep shooting these under the radar.