The Minerva Half-Life 2 Mod
Via GameSetWatch, an interview with Adam Foster. The creator of the Minerva Half-Life 2 mod talks about the reasons he's putting time and energy into a fan-made labour of love. From the article: "Single-player mapping ...does have quite a tradition, and sadly it often seems to be looked down upon by many gamers. It's somehow regarded as 'easy,' with multiplayer maps being the only true form of expression. I suppose the countless fullbright cubes packed with zombies must put off a lot of people, as do the endless bare BSPs which need to be run from the game console..."
You should play this mod. It's one of a handful of good single-player mods out there which is something I am much more interested than yet another multiplayer mod featuring zombies. It's played over a single map, and it's not very long. Ehh ok some good points, it's a good difficulty, the map is very well designed and feels very professional, and it's been written into the same world as Half-Life 2 is set, a good excuse to use combine grunts and their familiar technology. It's a sort-of followup to "Someplace Else", a mod for Half-Life 1 by the same creator, but having now played the previous mod I can safely say it doesn't really shed any light on this new episode. I personally can't wait for the second episode to be released. Grab Metastasis and some interesting backstory here: http://www.hylobatidae.org/minerva/phosphenes.shtm l
Ever hear of Dystopia?
Not sure if you would call it MUST-PLAY, but it is very good mod.
A few other fun ones: Hidden Source (fun and unique multiplayer mod), Eclipse was posted on slashdot awhile back - its good but only has an hour or so worth of gameplay, Garry's mod also, but everyones heard of that.
The slashdot member "Ford Prefect" is Adam Foster I think, anyway, give him your love, because it's a fantastic level he's made, and I can't wait for the next installment, bring it on Adam!