A X370 motherboard is a must for those looking to get the most out of the AM4 platform. There is a big chance that a B350 motherboard is more than enough for you in most cases, however if you want to run GPUs in SLI or if you plan on using a lot of hard drives, you're forced to go with X370 on AMD's side.
Biostar gives the impression that they're catering to these demanding users with the X370GT3. Unfortunately the board falls short in a couple of areas. The power circuit is not good enough for overclocking without any worries. Furthermore, only part of the VRMs is cooled, which is also not very convincing.
The USB 3.1 speeds also lag behind that of other motherboards, mainly in the read speeds. The audio quality also leaves something to be desired. The audio chip is quite old compared to what the competition tends to use, and - even more importantly - its performance is not up to par compared to what we expect from onboard audio in 2017. The scores aren't necessarily bad, however other manufacturers show that there's clearly room for more.
The biggest downside to the X370GT3 is the distribution of the lanes on the PCIe slots. The X370 chipset supports SLI and CrossFire with a x8/x8 distribution of the PCI-Express 3.0 slot, however Biostar has opted for another option. The second x16 slot, which is a PCIe version 2.0 one running at x4 speeds, runs through the chipset to the processor. In addition, the speed of the second x16 slot dials back to x1 speeds if one of the other x1 slots is in use. Every serious form of CrossFire (or mGPU) is basically not possible with these limited speeds. This means that the X370GT3 basically loses its identity, as Biostar did not include features that separate a X370 motherboard from simpler and cheaper chipsets. The X370GT3 is basically identical to the B350GT3 from the same company, however the latter is much cheaper.
If you're not bound to the features of X370, there many other more interesting motherboards for a comparable price, such as the MSI B350 Gaming Pro Carbon. Are you definitely going for AMD's top-of-the-line chipset? Then you should definitely shell out a bit more for a motherboard that actually offers everything that the X370 chipset is capable of.