It's easy to just upload a video and give it a decent title and hope for the best. Without writing a proper description, viewers and YouTube's algorithm won't be able to understand what your video is about and will most likely miss your video.
Don't drag on a super long introduction description. Just let them know what it is you are showing in this video. You also don't want to confuse people so you want to be clear and concise.
There is nothing wrong with a long description, as long as the description is about the video. Some people don't watch an entire video and prefer to read the gaming description to summarize the video.