Involving story, characters that mean something, and a simplicity of gameplay that never grows old
Fire Emblem is not only an excellent example of clear graphics, clean sprites and engaging gameplay, but is also an excellent example of where proper attention to story line can get you.
The simplicity of the gameplay concept (the 'rock-paper-scissors' idea) creates more room to break the rules. This opens up all sorts of tactical oppurtunities that can be exploited to the players content.
And sometimes to the players frustration.
I found the occasional death of a character to be a reason to reset and start the mission again - all because i didn't see the 'lancebreaker' sword the fellow was wielding.
This is by no means a flaw - in fact, it makes you say "i deserved that", simply because the concept is so simple that you occasionally take it for granted.
This leads me to the idea of characters simply not coming back once killed.
how many games give you the grace of a second chance (the Phoenix Down of Final Fantasy), or the idea of expendability (Advance Wars)?
In this, your high level Valkyrie dies and you can go on. AND, that healer/warrior has a name and relationship level to other characters. They respond.
Buy it, play it, then play it again to get the millions of tiny little easter eggs and bonus characters you can pick up. You'll want to get all of them.