I want to say mine is Kingdom Hearts III, and it's so close to being an easy choice, but a specific part of its ending severely undermined it for me.
Collection of Mana is also in the running, and Spider-Man would be too if it had come out this year (I'm only now playing it). Super Mario Maker 2 is also a blast, but I haven't been playing it for that long and it's not specifically a "first half of the year" release.
I'm also still playing Smash Bros. Ultimate constantly, like I genuinely can't get enough of it and Banjo-Kazooie coming later this year is just over-the-moon hype for me. Obviously, though, Smash Ultimate wouldn't count.
I'd really have to think about it, haha.