It's very easy.

Atmospheric, but running around in the dark eventually got boring, and instead of building up the suspense, it started to get annoying. The playtime is artificially slowed down by almost complete darkness — if the official episodes included only a few short sections with pitch black darkness, here it's half of the game. Because of this, it's sometimes unclear where to run to next and what to do — you do "the thing" and then wander around the map for ten minutes picking out things with your tiny flashlight, trying to figure out if anything was changed.

In the house where you had to collect batteries, I was really hoping that installing them would turn on the lights throughout the house, so I could at least get my bearings. Bummer.

Anyway, that's just my personal annoyance with one aspect of the mod; overall it's a high quality game that is very worth of a playthrough by every HL fan.