I know this is already going to draw some controversy and drive-by shitposts, but let me explain myself. Some people were disappointed in the Switch lineup this year, mainly after coming off of such a ground breaking launch with 2 GOTY contenders back to back. And while it's true that Nintendo put out some really amazing titles last year, if you look deeper at the Switch lineup itself in 2017, it wasn't as amazing as many make it out to be. In fact in some ways, it was actually worse than this year.
Now yes, you can argue that 2018 was fairly mediocre on the first party front. But third party support has been pretty great so far that it's able to make up for a mostly weaker showing from Nintendo. Here's the thing though, 2018 for the Switch was consistent. No major game released that many considered awful, but nothing that would really move systems in a way that Zelda or Mario would, with the exception of Pokemon and Smash Bros. towards the end of the year. You can even see that reflected in the sales. Switch hardware sales have been keeping a steady pace all year with only minor dips in the first half vs last year, and a huge boost in the Holiday season. 2017 meanwhile, had higher highs, but it also had lower lows.
Prior to the launch of the system, Nobody really believed in it. It seemed like it was yet another wacky Nintendo thing that could either sink or swim depending entirely on how much draw it's gimmick has. And considering the Wii U's failure, many bet on the former. It also didn't help that third party support prior to launch wasn't very good. Sega showed up with no games, Skyrim was already announced, and the only major third party announcements were SMT V and Octopath Traveler. Of course, the Switch would then proceed to blow away everyone's expectations, but things were rough for the first half of the year.
While most of Nintendo's titles were stellar, there were actually far less first party games for the Switch last year compared to this year. As Nintendo still had developers releasing a lot of 3DS productions at the time. Third party support was better than anticipated, but it was still mediocre at best, only really picking up towards the end of the year with Rocket League and the Doom/Wolfenstien II announcements. 2018 had less big Nintendo games, but Nintendo actually published more games for the Switch this year as well. Most of the year saw them release 2 games each month. So it's really a matter of quantity vs. quality. Sure, there weren't as many big AAA releases, but there were more games. Even then, third parties and indies still backed Nintendo up when there wasn't a lot of big releases. The Switch saw a lot more relevant third party releases/announcements this year vs. 2017. Fortnite, Street Fighter, Mega Man 11, Valkyria Chronicles 4, DBFZ, BlazBlue Cross Tag, Diablo III, Civ VI, and even more quality indie titles.
TL:DR - Point is, 2017 had less games, but it had bigger titles, 2018 had less big games, but it had a more good games and a bigger release slate. 2019 looks to be the best of both.