1-2-Switch is a selection of mini-games that focus on showing off the technology the Nintendo Switch's technology (and the dinky pads in particular) bring to the table.
There's a whole range on offer, showing off different aspects of the he hardware. The 'guess how many balls are inside the controller' game, for instance, does a great job of showing you how cool HD Rumble is.
Others show some quite innovative ways of using a games console. Quick Draw is a game that demands that you don't look at the TV while playing. Instead you stand face to face with a friend, waiting for the TV to bark "Fire" as you raise your Joy Cons toward each other and pull the trigger. You both immediately look at the TV to see an image of one person laying on the ground and the other still standing, following by a stat screen showing accuracy as well as speed. You wouldn't even necessarily need to be in someone's front room! It's the sort of thing you could play on a whim. Out with your switch in you bag, sliding a Joy Con off of either side of the screen and settling an argument.
There's also a sword game in a similar vein. One player raises a sword above their head while the other tries to clap their hands together in order to catch the blade before in lunges into their head. The swordsman decides when to attack, the defender needs to judge when that's coming. Simple rules that allow the players to play around with tactics away from button pushing in order to win.
There's a whole toybox of experiences on offer here, and 1-2-Switch might well turn out to be the Switch's Wii Sports.