I held off reviewing Lost Pig here because I beta-tested it, and I tend to feel some attachment to games I test.
Now that it's won first place in last year's annual IF Competition, though, and taken home the Best Individual PC, Best Individual NPC, Best Writing, and Best Game XYZZYs for 2007, and earned rave reviews from as far afield as the Onion AV Club, I think I can safely say it's not just my own affectionate beta-tester's bias at work: this is a fantastic game.
It's got neat puzzles, it's got a good sense of humor, and it's insanely responsive. All kinds of odd, esoteric, or silly actions are catered for, and that keeps the game entertaining even when you're temporarily stuck for a solution.
It's also, I think, a great starter game for people new to interactive fiction: the design is compact, so there's not much chance to get lost or need to map. The polish is so thorough that it avoids the sorts of parser frustrations that usually catch novice players off-guard. The implementation is solid and feels trustworthy. What's more, it's available for play online, so you don't even need to install an interpreter on your home machine.
Lost Pig does not break any surprising formal barriers, doesn't seek to provoke, isn't especially political; it is simply a superbly crafted entertainment combined with a gentle-spirited and charming story.