If it's a pokemon hack we're talking about, I'm not a fan of deep and mushy storylines involving pokemon, instead efficient gameplay matters a lot more. However, 'gameplay' is quite general a definition for me. It has to do with how the hack is carried out in its whole, without focusing on a single aspect of the gameplay. For example, pokemon hacks that focus solely on a good base plot and have great scripts to show it on, then wither out on the way as the battling is set aside, aren't so good. (always imo)
Eye candy can come later, or last, for all I care.