I'm a pretty big fan of the series, and I've played a good number of them. Got into it with Sacred Stones when a friend gave me a copy in high school. Went back and played 7 afterwards and liked it too. For me though, the highlight of the series is easily the Radiant Duology, they've got it all:
A great story with a well thought out setting and political background, a diverse cast of characters with great variety in personalities and all of whom have at the very least good designs, solid and fairly challenging gameplay that really expands upon pre existing trends built up by the previous games AND Radiant Dawn rewards you for playing PoR by reading your save data and bumping up the stats of characters who you had capped stats with! I really loved the mechanics of the series up til this point and the Radiant Duology really nailed everything down in my opinion.
On the other hand, to be honest, I was utterly disappointed by Awakening. The character and setting's writing generally felt weak with several characters simply being tropes (though I did like a few), the move towards a very typically anime art style was disappointing and overall hurt the visual designs of characters (though some, like Robin are still very nice) in my opinion, and the game has a poor sense of both unit balance and difficulty in my honest opinion. It was clearly designed with casual mode in mind, and while this isn't an issue so much in and of itself it makes Lunatic(and + if you're absurd) much more a dice rolling simulator than a strategy game which kind of misses the point of the series. Hard-Classic was an alright enough game to run through, but the Pair Up system felt a bit ham handed and poorly handled. It leaves many units a bit too weak to fight well on their own, but just on the verge of being so good they blow through everything, removing the challenge. Additionally the unlimited EXP grinding and money was not my thing, but that's neither here nor there. Ultimately though, what did it for me was making Radiant Dawn's battle saves a casual mode only feature AND making it so that enemy reinforcements spawn, move, and attack all on their turn of arrival rather than simply appearing as in previous games which gave you a chance to respond. This change makes some chapters downright frustrating to get through on Classic as you can have enemies simply appear and kill you in areas that you thought were safe, specifically the recruitment chapter for Walhart comes to mind. While most maps you can wager a guess as to where enemies come from, they usually have a large number of spawn areas and you have no clue what type of unit they will be, which makes even strategies taking them into account potentially null.
Keep in mind, I enjoyed some things. While I'm not a fan of the seal based promotion system in genral, the ability to not only promote but class change characters is an interesting inclusion and I enjoyed the system. I would like to see it a bit more well thought out and executed in future games. The ease of access to equipment was nice, though I preferred RD's built in shop to your camp. The expanded upon forging system is also nice and can lead to some enormously powerful weapons if you have the money. To be honest though, Awakening's best (and in my opinion only objective) improvement over the older FE's were these:
Pressing a single button to toggle enemy threat ranges is great
The new Ability system, while abuseable with enough time, is quite a step up from the limit system instilled in the Radiant Duo.
I'm not sold in the slightest on FE14 though if they manage to make the Nohr campaign truly as good as previous games tended to be then I'll gladly pick it up. So far the character designs are really irking on both sides so I'm not gonna hold my breath. The Hoshido side just seems like "FE:Awakening - More of the same **** if you liked that" so no thank you.