From the perspective of someone who enjoyed the game more than a lot of people here? Quite a few. I'm going by the definition that memorable means that I won't forget them in the years to come like I did with every Fallout 3 character.
Well, let's see. Curie is definitely going to be memorable. Captain Ironsides aboard the Constitution. Nick Valentine, for his history. Kellogg wasn't nearly as interesting as everyone made him out to be. As dumb as it sounds, Mama Murphy and Daisy (at Goodneighbor) were pretty intriguing once you found out more about them from other sources. I liked how they both promoted the use of finding out about a particular character from other people and data rather than just talking to them about it, wish there was more of it in the game.
And that's about it. Captain Zhao, everyone at the Institute, everyone in the Brotherhood, everyone in the Railroad, and everyone in the Minutemen were all somewhat interesting, but mostly one dimensional and their pasts are never expanded on. All the unique settlements were full of predictable cliches. All the companions I didn't mention were fun for a while, but not memorable.
Overall, it's a motherload of wasted potential. Wide as an ocean, deep as a puddle. But this topic of potential is a horse beaten beyond death.