My three favourite games of all time are Exile, The Sentinel and Zarch.
The Sentinel is an extremely weird game, but I loved it from the moment I bought the Commodore 64 version at KMart in 1987. I went on to love the Amiga version even more.
A typical view in the game. Image by: C64-Wiki
It was conceived and written by Geoff Crammond, who also wrote REVS (a great driving game on the C64), Stunt Car Racer (an insanely great game on the Amiga, which was best enjoyed by linking two Amigas together with a null-modem cable for multiplayer mayhem), and the Grand Prix series (a realistic driving simulation that started life as Formula One Grand Prix on the Amiga in 1992).
For me, The Sentinel is an outstanding game. It features a first-person view of a solid-3D landscape, which was incredible at the time. The ten-thousand levels are procedurally generated, which is something I’ve loved, from the days of Mike Singleton’s The Lords of Midnight and Midwinter through to Derek Yu’s Spelunky and Asobo’s Fuel (which Shamus Young has deconstructed at length).
The game mechanic is stealth; you must creep up on and ultimately destroy the all-seeing Sentinel, which occupies the highest square of the chessboard terrain, and which slowly rotates its gaze. You, of course, start each level standing on the lowest square. And, most unfortunately, you cannot move; only rotate.
To vanquish the Sentinel, you must absorb energy from the trees scattered around the level, and then use it to create robots that you may transfer your consciousness into, thereby teleporting yourself from square to square around the terrain. You gain height by creating stacks of boulders, and then creating a robot on top of them. In this sense, The Sentinel is a game of resource management, with trees, boulders and robots representing one, two and three units of energy respectively.
The trick is that you can only absorb energy from a tree, boulder or robot (when teleporting, it always pays to absorb the robot that you’ve teleported from) if you can see the square that it’s standing on. You must therefore work to increase your height, opening up lush new fields of tree-energy to mine. All the while, the Sentinel does the same thing; it absorbs energy from all bounders and robots it can see (including you), and uses it to create new trees at random places around the level. I loved this aspect of the game; it satisfies the first law of thermodynamics!
You can imagine how gut-wrenching it can be playing a level, with the gaze of the Sentinel upon you, watching your energy slowly drain away while you frantically scramble to create a new robot in a safe location, teleporting there only to watch your former self transform from robot to boulder to tree as the Sentinel consumes its energy.
Things get worse. If the Sentinel can see you, but not the square that you stand upon, then it transforms a nearby tree into a Meanie, which, when it rotates to face you, forces you to hyperspace. This consumes three units of energy, and transports you to a random square on the level that is lower than the one you were standing on. You could also initiate a hyperspace yourself, as a last-ditch attempt to avoid the full gaze of the Sentinel.
Victory was sweet. Standing above the Sentinel, immune to its gaze, you’d spend some time gloating before absorbing its energy to win the level. You’d then go on to a harder level, with the exact level number determined by the amount of energy you had remaining (so you’d jump more levels if you finished with more energy to spare). And because the levels were procedurally generated, there was no need to save the game. You’d simply write down the 8-digit code for the level you were on, and type it in the next time you wanted to resume your game (or, sneakily, try to reverse-engineer the algorithm, or enter level codes that you’d got from a friend at school, or seen printed in a magazine).
Later levels featured Sentries, which had all of the power of the Sentinel, but which stood on lower squares around the level. This made things even more frenetic.
Zzap!64, the premier games magazine at the time, refused to award The Sentinel a score in its review of the game, stating that such a wholly original game is in a class of its own, and therefore defies rating. Over twenty years later this is still the case. Everyone should play this classic game.