Prospekt is a for-sale HL2 Mod (That's the first gripe right-off-the-bat) its rather short about 3 hours or so (right above the refund window horizon that's the second gripe). The game starts off kinda slow and has a few decent puzzles here and there then it progresses into the shooting bits. It's been a while since i've played HL2 but it strikes me as a bit harder. Most of the levels are such that you enter into areas and fight a good group of combine forces and if you survive you fully restock on medkits then go to the next room. This requires you to get lucky and sort of do your best to engage enemies in such a way to jinx up the AI so they aren't constantly shooting you. The HL2 engine/AI doesn't really support this playstyle but the game makes it sort of work.

The highlights of the game are the cool voice overs, subplot to Corporal Sherman (From Opposing force) narrative heavy element. You also get new textures and environments which are pretty impressive. The game looks very good (for HL2 era standards anyway) and looks like the world of Half-Life

In the end this is a thing that feels like it should be made available for access (if not outright free) from those who own HL2.

Oh, it was a bitch to get going as well and i had to install Not only Halflife 2 but also Episode 2 and episode 1 as well to get it to work. Took time to figure that out.