Residual Point is a single player mod for Half-Life.
It has perhaps the longest (and most dangerous) training mission I've seen :D. Must have been a beta version map that wasn't used and so instead used for "training".
The mod itself is also very long. But while it has some good level design, in its first half... things start to change after you reach the pumping stations. From then on (including the surface levels) its pretty mediocre, random open couryards with some boxes fighting large groups of either headcrabs or grunts.
It gets pretty hard, which might be a good thing for some people but I found it to get pretty frustrating.
Like the introduction of a different low res Islave that can take twice as much damage, and a bigger reddish headcrab that takes alot of damage and moves faster. It seems like the mod was rigged to make it harder... so medium difficulty is actually pretty hard.
There are nitpicks to like some sections pretty much being copy pasted from Blue Shift, HL1, Opposing Force. Though I can only think of about 4 instances so that's not a big deal.
But the repeated voice acting from the previous games gets annoying, some custom voice acting would have helped this mod greatly.
It lacks a storyline or any scripted sequences so it gets stale.
The lack of a ending is the most disappointing thing about it. For such a long mod its a shame to see the creator sort of give up on it.