For me the biggest surprise of the Nintendo Switch was the amount of 3rd party support it got and some of the 3rx party games it got that had zero business running on a portable Tegra X1 device.
During the Wii U era and even before, the idea of some of these 3rd party games coming to a Nintendo system seemed impossible for me to believe. For example, even the simple idea of getting GTA on Switch was mind-blowing for me since we've never seen a 3D GTA game ever release on a Nintendo system for up until that point. Other games that shocked me heavily were Witcher 3, the Doom games, Apex Legends, Red Dead Redemption, Mortal Kombat even more simple stuff like Fortnite and NBA 2k. The idea of playing these games, many who've always neglected to ever release on Nintendo platforms like GTA releasing on the Switch surprised me.