LogFAQs > #950258183

Conquest has some of the best map design and general gameplay of the entire series. The story is absolutely garbage, however.
Birthright is fine. It's fairly average overall on all counts.
Revelation is pretty bad, though. Almost entirely recycled maps from the other games with worse balance than Birthright, and the story is just as bad as Conquest's.

I will say I generally enjoy most of the characters, though most aren't really top tier either, and it suffers from the same problem Awakening had with its characters (only to a greater degree) where there are just far too many who support too many other people so a lot of the supports are just lame. Three Houses did a hugely better job on this, thankfully.

Overall I'd say its just a painfully average FE game series, with the exception of Conquest's gameplay.