The modder decided to change the imps into alien slaves, on the surface this should seem like a straightforward swap as they both have a ranged and melee attack as well as looking fairly similar, however in practice this is a terrible choice as the key to defeating the imps is avoiding their projectile attack, something which the hitscanning vortigaunts lack.
This mod also contains no autosaves and as someone speculated earlier it may be to keep the doom style, but this doesn’t really work when there’s no pistol starting, but I won’t hold this against the modder, just remember to save frequently. Unless you’re extremely lucky you will die on hard through no fault of your own. Since the difficulties were changed to the same in Doom I assumed that I should play on Ultra-Violence (Hard) as this would be the “true” experience of the game – like in doom – however I’m convinced that the mod was not actually scaled for this difficulty. I’ll get the negatives out of the way first, because despite having a mostly frustrating experience with this mod there’s far more good than bad.
Half-Life: Crowbar-Deep in the Dead (Demo) | RTSL Menu