Whoo, jumped on this bandwagon way too late.
I'd like many of the features in the FE series that was actually UNIQUE. All three GBA FEs were pretty much spin-offs of each other, EXCEPT branched promotion in FE8.
Lover's system, inheritance and future generations - A reason why FE4 is so popular?
Branched promotions - This way, inheritance can work differently with the same pairing. Besides, I always liked it.
Magic/Weapon Co-Op - FE4 MageKnights and MageFighters were my favorite classes.
The extra excess of anticlimacticism - I'd like some suspense in a game.
Lots of classes and weapons - So far, seven types of magic was introduced (right?) and five types of weapons, not including Laguz weapons. Let's be extra ambitious, IS. Combined with branched promotion, an abundance of classes should have perfectionists like me stop worrying about class balance.
Bigger caps - Thracia 776 pissed me off SO MUCH. I say to FIFTY, DAMMIT.
Higher difficulty - Not like FE5 where reinforcements come relentlessly, but something you could work into. Like jacked-up bosses.
No broken characters - Sure as hell raises the difficulty, but I'll miss holy weapons (Call me, Narga~)
Extra-long game - How about 70 chapters? Just Kidding.
Fixed Arenas - Just so that you won't spend 200 turns.
Rank-less runs - Games are supposed to be stress-free. Why the hell would ANYONE tell the players to push themselves into getting that S Rank?
Unlockable characters in Epilogue - Now THIS is worth pushing for aftergame. However, no pulling FE6 or FE9s, where you have to beat the original game quite a number of times. I say the FE8 style, just goofing off here and there, until you reach your goal.
Better background storylines - No Navarres, please. I don't want none of that "came from nowhere, then vanished" crap.
The super story - The best and most climactic storyline. It's so good, it should be a book (or even a MANGA.)
Decent RNG - Why do I hate FE5 the most? Lemme think... Starts with an R... sounds like Tantrum Lumber Penentrator...
Put that together, we have a game that's worth waiting 10 years for. =.=