For games, thaaat'd be the gameplay.
And for FE, that means the maps.
Now, that said; if you want to talk about the story, plot, and characters of Gaiden, you've got a long hill to climb seeing as it's rather bare.
Story? Ash said it best...
Mycen: alm u cool
Alm: thx gramps
Lukas: join me pls
Alm: gonna kill guy brb
Alm: no u *kills
Celica: o no *goes on boat
Celica: *kills pirates and dragon goes to castle
Alm: I'mma kill Rudolf
Celica: pls no don't
Celica: i hate u *leaves
Alm: oh no i'm stuck on mountain
Jedah: save Alm kys to duma
Alm: *leaves mountain and kills rudolf
Rudolf: I'm your dad
Rudolf: kill duma
Alm: *metts up with Celica
Alm: Don't worry Celica, I'll crush these bastards! *kills duma
Celica: marry me
When a game can be summarized almost completely in such a joking and brief format I don't think there's much of a story to comment on .....
If I recall correctly, Robin/Tobin, Cliff/Kliff, and Gray each get a grand total of one text box of dialogue; and similarly Jenny/Genny, Mae/May, Saber, Valbo/Valbar, Sonia/Sonya, Dean/Deen, Boey, Noma/Nomah-- they get two or three across the entire game.
They have extraordinarily bare characters and almost no characterization because they simply don't talk to the player much at all!