While most people remember the NES for Mario, Zelda, and Metroid... or perhaps just being the system that revitalized the video game industry after Atari did their best to destroy it, there were actually a TON of games on that system that went by rather unnoticed but were still great games.
What made Solomon's Key so special is that it is a great game and is considered to be one of the most difficult games that was ever released on the NES.
The game was a lot like other platformers in the way that you began on a level seeking to get to the exit without dying. Soloman had the ability to create and destroy some of the blocks on the screen, the only exception being blocks that were directly below him.
this is one of the first levels of the game, and was already pretty tough
There were a wide array of enemies, and other than breaking the blocks out from underneath them, there was no way to kill them - if they fell on you, you died, if you jumped on them, you died. Basically the idea was to stay away from them at all costs.
The levels got to be really tough, really fast and there were a whopping 64 levels, many of which were very difficult to find by places blocks in not-so-obvious locations on a certain level. It is rumored that the number of levels was a homage to the Commodore 64. Keep in mind that this was well before the internet existed, so I can't even imagine how people found the secret rooms, almost certainly by sheer dumb luck.
The game was very long, even the best YouTube videos of total runthroughs without a single death take near an hour to complete and the best speed-runs (much much faster than mere mortals) still take 20 minutes.
Some of the levels were extremely frustrating because very specific timing was required in order to get past foes that were on a "circuit" of sorts and if you didn't get it exactly right there was no way you were going to finagle your way through.
I have to admit that for very young me, I didn't get very far in the game. I think the difficulty level may have explained quite a bit of the reasoning behind why this game didn't sell very well in USA nor was it recognized for being the fantastic game that it is until many years later. It was ported to the Wii and Switch years later.
I don't expect anyone to watch all of that, but you can tell by watching the difficulty featured on just the 2nd level, how extremely hard this game was. It was not well received by the USA audience as gaming was largely an activity for children at the time.