Just installed the Z77 Pro4 on a test rig and checked it out. My impressions are as follows:
1) After thorough examination of the board, I am very sure that these boards are produced at the same factory as Asus ones. This board has the feel of an Asus (even if you just tap the PCB on the ground, you will get the same sound!).
There are many common components with Asus boards right down to the VRM chokes, Nuvoton Super IO chip and capacitors.
The PCB is, however, slightly thinner than a good Asus motherboard. Not actually an issue, however.
Further proof: It even smells similar to Asus boards
2) The board is not standard ATX size, it is smaller. I had stated the same about Biostar TZ68A+, however this board is even smaller and yet packs more features without compromizing on cleanliness of the layout.
A big +1 to ASRock's engineers for this feat.
3) ASRock UEFI is highly developed but perhaps slightly less tweakable than Biostar's. The two UEFIs are roughly comparable and ASRock is slightly simplified compared to Biostar (which means, if you're a tweaker, go for Biostar).
4) Very high quality components and build, better than the TZ68A+ (I'm talking PCB and capacitors here).
5) System's running rock solid right now and I've been noticing that DPC Latency is minimum on this board compared to the Biostar. It doesn't make a huge difference performance wise but those millisecond spikes and hangs are due to DPC Latency.
6) Layout: I wasn't happy with PCIe x16 slot placement, because if you have a long graphics card, it gets too close to the HDDs. Other than that I really didn't have much to complain about.
7) ASRock Combo Cooler Option: This board supports adding any aftermarket cooler designed to run with Socket 775/1155/1156 and has the holes to fit all three types of coolers. This raises the choice for aftermarket cooling.
8) THX TruStudio Pro: It's the same as Creative's X-Fi software enhancements. Not a big deal actually.
9) UEFI System Browser: There's a cool option in the UEFI BIOS which allows you to check each slot and see what is connected there. Extremely good for beginners.
10) Addendum: Onboard audio is the same as TZ68A+, however the analog output has a clear difference. The output capacitors seem to differ and hence this board emphasizes the high frequencies and bass while keep mid frequencies less. I prefer the more balanced sound of the Biostar board (again, same audio chip: Realtek ALC892).
I think this board is good VFM. Remember what I said about the Biostar, that it's good but no Asus? I cannot say that for ASRock: This board seriously gives Asus and Gigabyte a good run for their quality (and money).
The bad? I think it has less tweakability than the Biostar TZ68/TZ77 series, but this is a Pro series board and it's the Extreme series that is known for OC ability.
Overall: I give it an 8.0/10.
If pics are requested I will have some up soon.
Side Note: I do think ASRock and Biostar are leading the way in providing value for money and I have zero issues about buying boards from these vendors again. That being said, with these brands you don't get a lot of value add extras. For example, ASRock includes a measly 2 SATA cables and no SLI/Crossfire bridge. Biostar includes those and has more SATA cables included but the PCB is slightly lower quality, for example (Sorry, no "powered by ASRock/Biostar" stickers!)
How thick the PCB is or the amount of copper only matters in terms of temperatures and if you're always carrying the board around in one hand, so it's not a big deal. However, the fact remains that you do get what you pay for. Each value brand has its pros and cons. For example: ECS has good build quality and horrible BIOS/UEFI that makes all of that worthless.