I recognize most of Titanfall's shortcomings. It's not a technical marvel, some people burn out on it really fast, the amount of content it shipped with was questionable, and it didn't deliver the genre-redefining "next-gen" experience some were hoping for...
But that said, it is so good. The parkour, the infantry vs. mech premise, the sound and art direction, the general feel of the game, they're all phenomenal. When things are going well, e.g. you're in a populated playlist and teams are balanced, it's just such an incredible game to play. Yes, the disappointment is real for some people, but there's a reason it's still one of the most played games on Xbox One. Plenty of people really like Titanfall for the reasons I mentioned.
If a sequel could greatly improve on the technical aspects, push that basic premise just a little bit farther, and add in a few more "hooks" like metagame stuff or real support for competitive play, I think we'd be talking about a game that people would really love and remember. Whenever I think about Respawn, I cross my fingers and hope that they're working on that game right now.