Super Mario Odyssey. Buy it.
/I read a review of Super Mario Odyssey which ended with the phrase "If you've got a Switch, you must buy this game. If you've not got a Switch, buy one and then buy this game".
I agree. It really is that good. Not that I'm anywhere near through it, but I'm enjoying every minute. Everything is polished to perfection. The game runs well on portable and on TV. The idea of having something this good that you can play on the train is really nice.
When I bought this game I did something I don't usually do with full price games like this. I bought the download version. It meant I could get started without a trip to the shops or waiting for a parcel, and it also means that the game is always present on my device. I've got a micro SD card in my Switch and the game takes up around 5.3G, which is not a huge amount of space by today's standards.
I'm starting to wish that I'd bought all my other games this way, it would remove the need to carry round cartridges. Perhaps a video game shop could over a scheme where they take your game media back and swap it for a download code. I'd go for that.