I've bought 3 systems at launch. The Xbox 360, the Wii, and the Switch. I was very close with the Gamecube, buying just a few weeks after launch, but I waited because I only had enough money for one game and I wanted Smash Bros Melee which didn't come out for a few weeks after launch. I could have bought the system at launch but I couldn't deal with having the system sitting there for like 3 weeks with nothing to play on it.
My first experience of a launch, with the 360, was by far my worst. I preordered 6 months before launch at Gamestop, only to find out 2 weeks before launch that Microsoft had massively overestimated how many they could deliver at launch and I wouldn't be getting my system for at least a month. That didn't work as at the time I was writing for a website and I already had several Xbox 360 launch titles sitting at home waiting to be played and reviewed. I had to have a system. This led to me getting in line at Target at 6:00 PM the night before when the store wasn't handing out tickets until 6:30 the next morning. I was 2nd in line for the four premium systems they had (the only ones that had hard drives). By 7:00 the premiums were claimed and by 10:00 the line was long enough that all 30 or so core systems they had were claimed too. It was around 30 degrees out when I got there but it dropped under 10 that night and it snowed half the night. It was pretty miserable, despite bundling up. A few friends who wanted to play the 360 did it with me though which made it more tolerable. Until 2:00 AM or so we all in line had fun, played handheld systems, it was kind of a party. Then everyone got tired and people tried to sleep and it got really bad. At 6:30 Target finally handed out vouchers for the systems to those in line and after the group who waited all night fended off a few people who showed up at the last minute and tried to steal them, we were able to leave until 8:00 when the store actually opened. Me and my friends went and got breakfast at iHop and then promptly got sick from doing so. We felt awful by the time we got the 360. Took it back to my place, hooked it up, played like 2 matches of Perfect Dark Zero, and then we all felt so miserable we fell asleep. It wasn't until the next day that we really got to enjoy the thing. All in all a pretty awful experience.
The Wii and Switch were less interesting. I preordered both and picked both up mid day on launch day. The Wii was from Gamestop, the Switch from Best Buy. In both cases the stores were somewhat busy still but lines weren't terrible and my preorder held. No updates for either, just took them home and played them. I may consider a PS5 at launch if it is fully (or 99%) backwards compatible, but only if I can preorder. My days of waiting hours in lines are long past.
