The only FE games I've played are PoR, RD and Awakening, and I enjoyed all three of them. I'm not sure what it is about the Tellius games, but they really sucked me in, I think the way it presented its world and different factions made me care a lot about its conflict and how it'd turn out, which made up for some of their gameplay deficiencies. This is something I felt Awakening could have done better, I didn't care about Ylisse, the political tension or any of the bad guys, I liked the three lead characters enough to keep me invested, even if they weren't all that deep, and it was also super easy to pick up and play, but there were a lot of things that felt like they were wasted or could have been done better. With the Tellius games I cared about the whole package, maybe more so with PoR than with RD as the new characters didn't do much for me, but I still loved both.
I'm not sure I'm ever going to delve much deeper into the series' library, there are so many games and once you start playing one it becomes a pretty big commitment, but I do have a lot of respect for its history. As far as its representation in Smash goes I do agree it's a bit much, and it's a shame that it's largely limited to sword users, but I'm willing to be a dirty hypocrite on that front if it gets me Black Knight lol.