The Sony F3 is a $13k professional camcorder, upgradeable via paid firmware upgrade to a $16k "even more professional" camera with a 4:4:4 S-LOG output. The Sony FS100 is the more compact, $5k prosumer version of the F3. However, despite the price difference, the two cameras share the exact same sensor. So are those initial negative reviews of the FS100 justified? It appears not. In the words of tester Alastair Chapman, "The FS100 is remarkably close to the F3. You would have no problems cutting between the two of them in a project." Here's a video comparison of the two:
In conclusion, Alastair notes (from his shoot with Den Lennie):
The FS100 performance is so very close to that of the F3′s (at 8 bit 4:2:0, 35Mb/s) that it is hard to tell the two apart. I believe the F3′s images are just a tiny bit richer, with about half a stop more dynamic range, in most cases it takes a direct side by side comparison to show up the differences. The range of camera settings and adjustments on the FS100 is not quite as extensive as on the F3, nor do the adjustments have such a broad range. However there is plenty of flexibility for most productions. If you don’t need 10 bit 4:2:2 then it is hard to justify the additional cost of the F3, both cameras really are very good. Despite some other reports else where I felt the build quality to be very good and the buttons, while small, are big enough and well placed... In either case these cameras can produce highly cinematic pictures and I see no reason why you could not shoot a great looking feature with either.
My feeling is that Sony has hit the right price points with each camera: if you're doing guerilla filmmaking with your own kit, the FS100 is the way to go (get an adapter and pair it with your existing DSLR lens kit), but if you're going to be on a bona fide set then the F3 will be worth the step-up in price. And if you're going to be doing really guerilla shooting, then there's always the $1k DSLR, with its lack of good audio inputs and other issues to fiddle with. Any of the three is a great option to have and it's a wonderful time to be putting together micro-budget features.