Fun, very challenging, and much more enjoyable than the movie.
The graphics are big and detailed, usually traits that aren't found together in a NES game. The bosses and levels are well-designed, although more way-points would have helped keep the frustration down. This game is not easy and requires a good memory to not die over and over and over and over again. Patterned attacks are the key to winning fights, because melee tactics do not work. Gizmo, though a stud, isn't exactly a brawler, really.
The music is a little trippy, mixing fright, urgency, and weird new age sounds. I was always too busy trying desperately to not die to pay too much attention. The sound effects are few, but specific enough to not be confusing.
Controls are tight, which is good because of the difficulty. Gizmo attacks and manuevers responsively, and without it he wouldn't make it to the spider gremlin. Weapons include the paper clip and the match-arrow, just like the movie. These are needed to dispatch the copious bad guys, including bats, bugs, rodents, gremlins...it's a mess that only Gizmo can clean up.
The story progresses through cut scenes, a-la Ninja Gaiden, and follows the script from the movie. Basically, Gizmo has to rid a large building of gremlins before they spread into the outside world.
However you find Gremlins 2, give it a few hours of your time to remember what a good NES game was like.