Fort Driant by JPL
Note: there are two versions of this map, a VISed version with some HOM problems and an unVISed version without those problems but which will run slowly on older systems. For further details see the readme.
JPL's latest long-vising handful of a map is Fort Driant, in which he brings some of the style of Half-Life (the first) to Quake. There was obviously a lot of work involved in this; the initial outdoor scene of the map is a good indication of this, as it contains replicas (brushwork, as in the original) of the trucks and forklifts from Half-Life, as well as a detailed crane with a really cool nailgun secret. The textures aren't very Quakey, but they have converted more or less intact, and the theme of a base/bunker is pulled off well in the setpiece areas.
Once you get inside the base, things change a lot (and not necessarily for the better). You find yourself in fairly dark, cramped bunkers, and at the mercy of Quoth base enemies who can take shots at you through small openings in the walls. The various hallways aren't all that distinct (a problem I had with the original Half Life), so navigation isn't that easy although you will probably not actually get lost - the issue is more excessive backtracking to figure out where to go. Later, the hallways are better-lit, a sort of bluish futuristic appearance (functional details also make appearances in places, or as close to it as can be managed in a map this big with Quake's block-favouring brushwork). Some of the rooms in these hallways are look decent, and the whole thing certainly is a challenge with many enemies and quite a few of those Quoth-level base foes. These things are certainly good, but there are numerous drawbacks to this style of gameplay, which by its nature (many closed corridors, where you can't see anything but the hall you're currently in) is confusing (no real idea of where you are relative to the layout as a whole) and frustrating (similar visuals in most places, backtracking).
Once you reach the back of the base, the confusing corridors open up to a gigantic setpiece clearly inspired by an area early in Half-Life: a huge silo, surrounded by walkways. This area definitely looks cool, and it's even cooler that you get to go on top of it and that numerous beams/details cast asymmetrical shadows down on the whole scene. You approach this structure from many angles, and you must beware of enemy sniping here. A lot of mileage is gained from the layout, as the exit is actually back outside the base, so you have to go through again.
This map is a mixed bag; it is ambitious, large, challenging and unique, but it can also be bland, confusing, slow, and monotonous. It seems like the amount of hallways is not really necessary, and even that the main function of the hallways area (other than imitating this aspect of Half-Life's design) is really just to connect the two setpieces. It might have been better to split this level into two, or even three separate maps. The nature of this map means that its virtues/limitations will be appreciated differently by each player; give it a try, and see what you think.