I'd say something like Radiant Dawn.
Difficulty spikes to keep you on your toes
Insane boss stats
Defense-oriented maps as opposed to the usual "seize" or "route the enemy" (Elincia's Gambit and Blood Contract are some of the best maps in the series IMO)
Convos that are not support convos but still fun to watch
Ledges. Yep, ledges
Canto that allows you move again after attacking
Rescue command
Well-written story
Memorable units...I mean, Radiant Dawn has a large roster (probably the largest) and yet all of the characters are memorable
But then, FE5 has also some of these qualities that maaaaaay be controversial to a lot of us even though I like them:
Ambush spawns
Capture and steal mechanics
Leadership stars
Levels that can be cheesed out in absurd ways
Low stat caps
Scrolls
Broken weapon that stays
RNG that can never reach 100%