This was my first PC build! I'm glad that I did it myself because it wasn't that hard and it was an enjoyable experience. I took my time with it and enjoyed the process. It took me about 11 hours to complete the build, and the only tools I used were a Phillips head screwdriver and a Swiss Army Knife.
I primarily built this computer because I want to game on PC, record gameplay, and make videos for YouTube. I was using a laptop and an Xbox One before, so this PC is a nice step up from both of those systems. Even though BF4 is the only game I've played and recorded so far, I'm very pleased with the results. (Over 100 FPS on Ultra graphics settings.) I enjoy using this PC for everything else, too. My laptop still has its uses, but I'm glad it's not my primary computer anymore.
I probably could have spent more time picking out my parts, but I don't regret a thing. I just wanted to make progress and not fuss over little things. I took the same approach when putting the PC together, too. I didn't want to overthink it and make it more complicated than it needed to be. I got stuck a few times, but with some experimenting and research, I overcame every obstacle within 20 minutes.
Now that I have my entire PC all set up with peripherals and everything, I will buy a new desk. (My current desk is cheap, old, and too small for the PC.)
EDIT: Kind people in the comments section have pointed out that I can't overclock my CPU because of my motherboard. I would have gladly spent more money on a motherboard if I had known that this was going to be an issue. I don't really have a need to overclock yet, so I'll swap out the motherboard at some point in the future probably. This is my only regret so far.
Edit 2, 9 months later: At this point, I'm not playing games at all. I love my whole PC setup, though. I still use my laptop often, especially since I put an SSD in it, but my main PC is better in every way. The sound quality, monitor, and speed are far superior than what my laptop offers. I love the desk, and I love the look of all the lights even though I made no attempt to make anything match.
One thing that I surprisingly love the most is the mouse. I'm sure there are plenty of mice better than the one I've got, but it's the best one I've ever used, and it makes me loathe the use of a trackpad. A big, good mouse, is something I will never go without again. Because of this, I bought a bluetooth mouse for my laptop.
Upgrade paths - Larger, higher resolution monitor and better chair.