There's a cave system nearby, rumoured to be full of treasures. You set off to explore it and collect the treasures, and hopefully live to tell. There's no other background, an no real story -- it's just a travelogue. There are some beasts to employ or conquer, and some dwarves, a troll, and a pirate to reckon with.
Adventure is the grandaddy of all adventure games: the game that created the genre and gave it a name. As the first game of a new genre, it has many shortcomings but it also has some impressive strengths.
The world is very well presented. The prose is effective and unrepetitive, but with the occasional purplish flourish to liven things up. The major presentation fault lies with the simple verb-noun parser.
There's no story, and your character is left undescribed. The other creatures you meet are simplistic, although they're a natural part of the environment. The cave lacks any thematic cohesion, some reasoning to bind the individual rooms and objects together. Despite this, the challenges are a natural part of the setting, with no excessive contrivances used to build a puzzle.
Adventure is a good puzzle. There are some silly challenges, but once you get the game's sense of whimsy even these are fun: they're witty, never tedious. Gameplay is very open. This leads to minimal connectivity between the challenges, but the challenges tie in naturally with the objects. If something looks like it should work, it does, frequently in several places. The puzzles are surprisingly clever: they often require a leap of intuition rather than careful attention to clues. The game isn't really all that difficult, but if you do get stuck you might so remain for a long time. Even the mazes are cleverly presented, using the text interface to advantage.
The gameplay is surprisingly well designed. If there was a good story to go with it, the first adventure game would have also been one of the best. Adventure is a good simulation of its world. It gives you a strong feeling of exploration and, um, adventure.
Solution by me.