Pick any licensed game at random, whether it be a game based on a movie, TV show, cartoon character or whatever, and there is a 99% chance it is going to be crap. However, it's not 100%. Every now and then there is a gem of a licensed property. Hello Kitty World is one of those and it has a surprising lineage.
Hello Kitty World is relatively obscure for a number of reasons. There is the above mentioned fact that it is based on a licensed property, leading the average buyer to likely believe it is some crappy kids game. Then there is the fact that it was released very late in the life of the NES in 1992. Finally, it was never released outside of Japan.
However, Hello Kitty World was actually developed, at least in part, by Nintendo themselves. In fact, the basis of Hello Kitty World is Balloon Kid on the Game Boy. Balloon Kid is a sequel to Balloon Fight which is a fairly well known arcade game by Nintendo. Balloon Kid adds to that relatively basic arcade experience by turning it into a side-scrolling, flying platform adventure game. Hello Kitty World for the NES enhances the game further and adds the licensed characters.
The premise is that you must navigate through the sky which contains various enemies, floating with the help of balloons. If an enemy pops your balloons, you will fall to the ground. You can also release the balloons at any point to drop to the ground or on top of an enemy. At that point, you can inflate new balloons to float into the air once more. Enemies can also kill you directly and if you land in the water, you also die. There are various unique play mechanics that make this a pretty good platformer. While Hello Kitty might not normally fall on your radar as a character you want to play in a video game, Hello Kitty World is an excellent platformer and should be tried by anyone who enjoys the genre.
Of course, to play Hello Kitty World your options are currently pretty limited. As far as I know, there have been no re-releases and licensed properties rarely get that opportunity. Since this was a Japan only release, you will have to find a cartridge and a Famicom or suitable converter if you want to play this on real hardware. Or you can go the easy route and fire it up on an emulator instead.