I feel like what's so great about the BTTF movies is that they feel cohesive like a trilogy. With The Matrix it definitely felt like the first one stood on its own and the rest was just milking it, and going off the rails. I guess you could sorta make that case with BTTF (first being on its own, 2 and 3 being connected more), but I think they added just enough things to make it flow nicely. Like how BTTF already ended with them flying away in the car, which obviously is the start of nr 2. I also love some of the foreshadowing in BTTF2, when Marty goes to Biff's casino in alt-1985, he sees footage of Mad Dog Tannen (from BTTF3), which was a really nice hint in retrospect considering we didn't know during BTTF2 that they would go to the western in nr 3.
I think you could look at the story arc over BTTF, BTTF2 and BTTF3 and it feels like one long journey. With The Matrix I feel like the original just feels so different from the other two. The first was so great because of tension and the fact that the agents were actually a serious threat, and if you fought them, you would most likely die. In the sequels they became a joke and Neo could basically fight a thousand of them by himself. They just had such a different feel to them, whereas BTTF has the same light-hearted feeling and spirit throughout.