I've built many (>10) computers over the years and my experience has been generally good.
With that being said, my 2¢ (this won't matter to you, Harmy) is to watch out for noisy PSUs and noisy motherboard designs. Most PSUs–even expensive ones–are noisy buckets of crap. It's supposedly a basic fact of SMPS, but I knew nothing about this prior to building my most recent PC and the noise on the PCI-express bus was so bad that you could easily see it in my test captures with my Blackmagic Intensity Pro. (This setup has been scrapped for parts. None of these noisy captures have made it into the wild.)
The real kicker is that there's no easy way to know if your "expensive" parts are noisy buckets of crap or not. It's a crap shoot (pun intended).