A Crimson Spring, Robb Sherwin's entry in the 2000 IF Competition is, by far, my pick for #1 underdog of that competition.
It's not a writing masterpice that Kaged is; it's got no clever puzzle that Ad Verbum does; heck, it even has no in-jokes that made Being Andrew Plotkin immensely popular. What it is, though, is an incredibly atmospheric, fun superhero IF game that is chock full of as much multimedia extravaganza as the interpreter HUGO allows.
So what exactly is so great about A Crimson Spring? Well, I'll let the great capsule review by Dan Shiovitz speak for me: "I assume you know it's a superhero game. It's, I guess, the first serious superhero IF game that I've played (or as "serious" as superhero games get -- the villains all have stupid names like "Iron Lung" and "Snowman" and your girlfriend fled the USSR because they wouldn't let her practice her religion and shape-changing in peace or something). But it's got that gritty thing going on, the mean streets of the city, uncaring cops, moral dilemmas, blah blah. Pretty well-handled, and the music is just the right punk-ass soundtrack to make it work (the pictures I can take or leave, but, hey, I like a picture). Oh, there's also an honest-to-god fight scene in the game, with hit points and everything, that feels like Sherwin wrote this great combat module and then didn't want to throw it away, even when it no longer fit the story."
In short, A Crimson Spring simply rocks. It even has great homemade songs and campy graphics to enhance the atmosphere in addition to the gritty writing. A word of warning, though: if you like "perfect" IF, I.e. games that are competently coded with no grammatical or spelling errors, A Crimson Spring isn't your game. It's rough, it's consistent, and it has quite a few annoying guess-the-verb puzzles. On the other hand, if you love IF the same way I do, i.e. for the excellent writing and a great atmosphere that immerses you in the author's world, then by all means, try it out. It's one of the most atmospheric IF I've ever played, and the fact that this is a superhero game, albeit a "dark" one, counts a lot :) Two thumbs up!