I've had the first and second generation Raspberry Pi Bs, Raspberry Pi Zero W, and now two Raspberry Pi 3B+s. My initial experiences were a bit disappointing, as whilst the software support is great, the board seems more power temperamental than it used to be. I was fully aware of issues with the voltage going below 5v, but was surprised to see that this was still such an issue with the modern Pi, moreso than that of older ones. I ran it from a 5.02v supply with a short power lead, and had undervolt issues. I then tried a power supply that I normally use for rPis, which is tuned to 5.2v under load, and it had issues also, with several USB leads, including some good quality high amperage capable ones.
I then connected to the GPIO header, and everything was fine. I was surprised at how finicky this generation is, and how it would actually overheat because of a undervolt during boot, so would be locked at a lower CPU frequency from then onwards. I also tried the genuine Raspberry Pi power supply (didn't have those before now)... and that was fine also. Other than the power issues (which surely the onboard PMIC should be able to manage better and prevent being so much of an issue?) this is a great board performance and stability wise.
Other than the power issue, the only other complaint I have is that it does seem to run hotter than the previous generations boards when basically idling. But I suppose this is the trade off for having more performance available. Having the onboard Wifi and PoE capability is well worth the upgrade, as long as the possibility of some active cooling being needed is taken into account.