I got the special edition so I've already played through all 3. Gameplay is awesome, story is decent (miles better than Awakening, though), music is terrific. The My Castle thing is pretty nifty, I hope they expand on that idea in future games.
I think between just Birthright and Conquest, I prefer Conquest. It's hard to say, really. The story of Birthright is better, but I like the more traditional FE style of Birthright. Revelation is pretty cool, and the story certainly makes more sense than the other two, but if I were to replay just one in the future I'd probably stick to Conquest.
I like that there's so many new skills and I'm really glad they changed up the whole "pair up" thing from Awakening, so it's not so overpowered.
The only real complaint I have is I don't like the way the, uh... character stats/inventory/menu thing on the bottom screen is laid out in battle. I don't like that stat buffs are colored black when they were always like blue or green before (it took me a long time to figure out that wasn't a debuff to my stats). This is also worse considering weapons and skills change stats so much now. I mean you can just touch the stat and the little infobox comes up but I still don't like it. I guess it's not that big of a deal, it just seems weird that a 4th of the screen is dedicated to the character portrait. And I don't like the art style. But whatever, great game(s). Might be my favorite in the series.