Click this image to see what the gameplay looks like.
Have you played Portal? You could say it's a sort of distillation of requisite adventure game elements (without many of the sometimes silly frills that come with typical adventure games) combined with classic action (jumping, timed challenges, precision). At a glance it looks like a pure puzzle game but it does have a strong underlying motivating narrative which, like Ninja Dodo brought up, is often implied. In this case it's a series of one way dialogs with the A.I. (
"And there will be cake."), and 'tableaus' you discover through exploring the gameworld (
"The cake is a lie...").
Portal is being hailed as a critical success (despite its brevity) for its design and wit, but I think its commercial impact has more to do with its being a part of an awesome package in The Orange Box (Half-Life 2, HL2: Ep. 1, HL2: Ep. 2, Team Fortress 2, and Portal).