Tallima: Find games you like and play them until you're done.
Many games aren't worth completing. That's not your fault. They either stop being fun, become overly complex, don't give story updates and you forget where you're at, or they are too long and don't given enough variation or growth in gameplay.
So enjoy aying your games. Relish the ones you conquer, but enjoy the ones you don't finish too. Many games have an awesome first few hours but become worthless to keep on playing.
That's true. Most games can't hold up the quality for long and get boring really quick. What is a game with 100+ hours gameplay time worth when you are doing most of the time the same grinding crap or doing uninspired sidequests like "kill the monsters over there" and "bring this to person XY"?
Back in the days, when I was younger, I played a lot of such games and I had the patience for that but meanwhile my taste changed, maybe because I also don't have so much time I can spend into gaming anymore.
Today for me a game has to have a high immersion by it's tight told story woven around a predefined character. In most games today you can often build your own character but this character is interchangable, not really tightly fited to the story.
So I mostly play adventure games today. Not necessary for the gameplay but for the story. When I get stuck for too long, I use a walkthrough.
The only open world games that kept me playing are The Witcher games, most of all The Witcher 3, because even the sidequests have their own good and interesting stories.