Most Atari 2600 games take a simple idea and run with it, and that's exactly what Dark Cavern does. I would not say games like these are bad, but they aren't particularly good, either. Dark Cavern, like so many others on this ancient 8-bit system, fall neatly into the category of "Games that wouldn't hurt you to try if you're already playing around with an emulator or collecting 2600 cartridges anyway, but you won't be missing much if you don't play them".
Dark Cavern combines the single screen maze formula of Pac-Man with the man-against-robot aspect of Berzerk and adds its own unique twists. As an armed man in a maze, you must run around and shoot robots that enter from holes in the side walls. The robots can shoot back, of course, and the net result is that it feels like an Atari 2600 version of a paintball game.
At first, the robots are quite simple and stupid. They move slowly and only shoot in the direction they are facing. Eventually, when your score reaches about 25,000, robots that can turn their heads and shoot in any direction enter the fray. You will only progress by learning to get behind them or by ducking into a corner, shooting, and quickly ducking back out.
The game limits your ammunition, but occasionally a gun appears in the maze that will give you more bullets if you can reach it in time. It's interesting how running out of ammo was never an issue for me since it's pretty easy to play conservatively. Although there are also spiders that paralyze you and wavy blobs that steal your bullets in addition to the robots, these creatures aren't worth any points and move so slowly that they are best ignored when possible.
Dark Cavern's play control takes its cue from other maze games in that your man doesn't stop moving until he hits a wall. This makes it tricky to use the "ducking around corners" method since sometimes your character will keep going when you wanted him to stop or turn the other way. Deaths are inevitable in arcade games, and especially in maze games will you eventually be killed by getting trapped in a corridor with an enemy coming from both sides. Dark Cavern is no exception.
That brings me to the most relevant point I can make about Dark Cavern: Despite any nuances in the gameplay, if you've ever played Pac-Man or Berzerk (or a game like them) before, you will probably feel like you've already done this. Because the maze never changes, there is hardly any sense of progression, which makes maintaining prolonged interest difficult.
There are some tricks you can learn that will more easily help you achieve 200,000 points and beyond. I won't spoil them, since figuring them out is the bulk of interest here. However, if there was ever a time when it meant something to have the highest score on Dark Cavern, it's probably long since gone past.