The only thing that comes to my mind when asked to describe this is "what were they thinking?!"
In case you're wondering whether or not Back to the Future II & III was simply a quick cash-in to the later movies of the hit trilogy or in fact a true sequel, yes, there was a Back to the Future I for the NES. Also published by LJN Ltd., it was also a truly horrid game. Somehow, someone, however, was convinced that a sequel was in order, and the end result was Back to the Future II & III. The gameplay is greatly expanded from the original, but hardly improved upon and suffers from the same lack of development forethought.
As one might expect, the game loosely follows the plot of the movies: returning to Sunnyvale Valley, circa 1985, Marty McFly finds himself in a world transformed by his arch-nemesis Biff Tannen, who had used information from the year 2015 to start his own personal empire and transforming the little town into a run-down slum. The key to Tannen's power, a future sports almanac he used for horse betting, has been safely tucked away and the only way Marty can destroy it and restore the timeline is by finding various objects scattered around time by time traveling to 1955, 1985 and 2015 and return them to their normal place. Any similarities to the movies end there, as the actual game bears very little resemblance or tie-ins the movies. Immediately identifiable are the classic DeLorean, Marty's futuristic hoverboard (which is strangely also available in 1955 and 1985) and a smattering of background images taken from or at least vaguely resembling various locales from the movies. Beyond that, Back to the Future II & III could very well be any generic platformer - understandably, practically all of the enemies had to be invented for the game as few from the movies are suitable for a direct translation, but many of the enemies simply don't make any sense. Walking hamburgers, deadly lizards raining from clouds, kamikaze birds, oversized slugs, jumping slime, flying ghosts and what is almost undeniably a rip-off of Super Mario's Koopa Troopa provide a sample of the nonsensical enemies that populate the three timelines. Attacking them, as in most platformers, involves jumping on them, although I encountered some hit detection problems as what looked like a solid, safe hit resulted in a lost life. Many enemies drop power-ups when defeated, such as fuel pellets to fuel the DeLorean, keys to access mini-games and shooting pellets which allow Marty to defeat enemies from afar - very useful especially considering the questionable hit detection. Occasionally these enemies will be placed inconveniently and will present a major obstacle in the way of power-ups, especially faster-moving enemies on short ledges, but for the most part they're easy to defeat and just as easily bypassed, adding no real challenge.
The true difficulty in the game lies in the few and far between availability of power-ups, long, complex level design and an overall tedious experience with very little gameplay value. Each of the three timelines is also divided into a dizzying maze of streets, with many streets accessible only from certain timelines. While the street design opens up many exploration opportunities, the various streets quickly become repetitive and boring, featuring little in the way of variation other than some curious buildings in the immediate background. Advancement in the game revolves around finding keys which are either placed in difficult-to-reach spots, or, more often, dropped by certain enemies, which are then used to open rooms into mini-games. Completing these mini-games wins the player one of the various objects that must be collected to destroy Biff Tannen's future almanac, which must then be placed into rooms scattered throughout in well-hidden locations throughout the game. The mini-games, like the overall game itself, are tedious, repetitive, and frustrating, and a player can easily expend all of his extra lives trying to complete a single mini-game. Finding the mini-game rooms in the maze of streets scattered throughout the timeline is a frustrating experience on its own. Once the mini-games are completed, finding the correct rooms becomes an even more frustrating experience as these rooms are very well hidden in such places as manholes and pipes, many of which contain dangers such as hidden enemies or falling manhole covers. To add to the frustration, the name of the object that belongs to that specific room must be unscrambled, and an incorrect guess results in that object being returned to its mini-game room, which must be completed all over again. Given the depth of the street and timeline mazes and the various mini-game rooms and well-hidden object rooms which must be found, as well as the lack of save feature, it quickly becomes easy to have to spend a number of hours just to complete the first part of the game. Once this part of the game is completed, the "III" part of Back to the Future II & III begins; unfortunately I have only been able to reach this part of the game once or twice and am unable to elaborate further.
The sound and graphics are subpar, even for a 1990 NES game. The worst of both occur in the 1985 timeline, when understandably the developers were looking to recreate the burned-out slum of the alternate Sunnyvale Valley created by Biff Tannen's corruption. Unfortunately, what the developers came up with to reflect this atmosphere is an incredibly ugly level design and equally ugly background music. The 1955 and 2015 level designs are far less visually and audibly offensive; the background music for 1955 is a generic synthesized 50's beat while 2015 features a jazzed-up version that's also featured as the game's intro music. Level designs for both timelines are generally pleasing if bereft of detail. The far background drapings show some signs of sloppiness, as backgrounds meant to transition from forests to town will feature half a tree dissolve into the air. Sprites are adequately rendered although they could use vast improvement, especially the player's Marty McFly sprite which just comes off looking like a generic platformer character. Sound effects are awful, especially the annoying siren warning the player of homing enemies.
Overall, the incredibly long, tedious, maze-like repetitive nature of the game, its lack of save feature, and visually and audibly unappealing game design with little connection to the movies it tries to represent make Back to the Future II & III a game best left gathering dust on used game store shelves.