I don't hate any FE, and I consider them all good games for various reasons. However, 3 of them I always think twice about playing unless I use an odd fix for one of them
FE12: FE3 was amazing... at the time of it's release, but while it's dated af now, it's still my favorite FE for some of it's unique mechanic ideas, fleshing out more of Tiki's character, and featuring quite possibly the most steller character development I've even seen in the series in how Marth is handled. FE12 "fixes" it's datedness by removing the mechanics I loved like Dismount and Manakete tranformations entirely, and RUINS Marth's character development thanks to Kris. I can accept a lot of pandering from FE avatars, but when they ruin a part of a story I really liked, I get pissed. I get really pissed, and it's why whenever I go back to FE12, which is still fun gameplay wise even if I consider the original much better, I play it in Japanese so I can't understand the character development Kris is stealing.
FE10: HOLY FUCKING HELL, where do I begin? This game can easily be summed up by one word, clusterfuck. Part 1 is POR all over again, which admittedly bores me because it's not like we went thru this same shit last game just for the neighbor's country, I love Part 2's storyline, but it's maps quickly turn into a waiting game for me, and just fuck all of Part 3 and 4. It's a shame I have these issues with it tho, because I love branching armies, it's why I liked FE2 and TRS so much, but this really wasn't how to do it. I still recommend it for those who liked Tellius and don't mind waiting thru Other Phases constantly tho, because it is fun at points.
FE4: Oh boy, this game. I really want to like this game a lot more than I do, and I'll be honest, if it wasn't for three certain things, I'd be a lot kinder to it, but the backtracking is obnoxious, doubling and critting not being a universal ability bothers me, and it's pacing is absolute shit. I can recommend it for the soundtrack and Arvis' character arc, but not much else unfortunately.