I see the Lego comparison and I admit, when I built computers when I was younger I did that exact comparison.
Nowadays I would say it's more akin to building Ikea furniture than Lego. It can be daunting, especially the more expensive you go, and depending on one's situation it might even be better to have someone else do it, but if you do build it, it's very rewarding. IIRC the CEO of AMD made that Ikea comparison and it's a lot more apt IMO.