Sumatra puts you in probably unfamiliar location — the largest island fully part of the country of Indonesia — doing a probably familiar activity: Touring an area, and making a record of what you've encountered in a notebook.
Below you see my notebook at the end of a five-player game. I saw a few people, a couple of crafts, a trio each of flora and fauna, and (most impressively) two volcanoes, along with an assortment of equipment. I ignored wifi, GPS, and villages in this game because no matter how much ground you cover on a trip, you still can't encounter everything.
For the nine types of tiles, most of them score in a different way: people rewarding the player who has seen the most (and punishing the introvert who met the fewest locals), crafts scoring for volume, flora and fauna scoring only for the highest item when paired (and otherwise not scoring at all), and so on. The game begins with a draft of randomly drawn tiles so that players have a stake in one or more fields of exploration, then you set off around the island, which is when the game truly begins.
Your tokens are joined on the island by a tour guide, and when your group moves to the first location, you draw a number of tiles from the bag. When you're with the guide, you can either stay put — exploring the current area, if you will — and draft a tile for your notebook, or you can ditch the group and race ahead to the next location. You don't get to take anything this turn since you're traveling, but next turn, the tour guide will come join you, with all of the remaining tiles from the prior location being moved to the side and replaced by new ones, with you getting first choice. Hey, you're rewarded for your adventurousness! Hope something appealing turned up...
If someone has moved to the next location, then you know the tour guide is going to join that player on their next turn, so you don't have much time left in the current location. Will you also move ahead to the new location, skipping a tile now for a choice later? Or will you stay put, grabbing one of the remaining tiles before they're pushed aside, while knowing that next turn you must move ahead while claiming nothing? That's the dilemma you face constantly: the known bird in the hand, or the unknown and possibly better bird in the bush.
As you draft tiles, you start focusing your attention along certain paths, both to score points at the end of the game and to grab bonus tiles for reaching some combination of things first. The fewer players you have in the game, the more you can attempt to do — although of course everyone is trying to do that, so you'll still be bumping elbows for this bonus or that, still eager to move ahead for the first crack at whatever's next while possibly ceding ground to someone else with what you left behind.
The two-player game differs from play with 3-5 as you use the reverse side of the game board with fewer tiles drawn at each location, which means that not all one hundred tiles will be drawn, which means you're never guaranteed to complete your craft collection or find the wifi token you desperately need. The decision to stay or go can become even trickier because if the opponent moves and you don't, then you're giving them the first two picks from the next lot.
At heart, Sumatra is little more than that choice over and over again — while also involving probabilities for what might turn up and mind-reading in terms of figuring out what others might take — yet the game is compelling as a model for both vacation tours and real life, which is also you confronting that "stay or go" question over and over again. Every choice you make to do something means you have simultaneously made a choice not to do ten thousand other things.
I talk much more about the game, which I've played eight times on a review copy from Ludonova, twice each at all player counts from 2-5, in this video overview: