All five from gen 1 are really great, especially mew/mewtwo and zapdos.
Then suicune and ho-oh are excellent.
In gen 3, where legendaries really started to become prominent in the plot and grew in number, the legends were OK except lati@s (they sincerely look like shit, sorry fanboys) and, to a lesser extent, Jirachi (so obviously designed for promotion events that it hurts, it's like a santa pokémon for you baka gaijins). Deoxys has a really cool concept.
Then on to gen 4, the true downfall of legendaries.
Their numbers exploded : the main trio (who all look like retarded spiky designs with absurd proportions, obviously created by an edgy 12 year-old), the 3 awful fairies, Arceus is bland as fuck + same problems as the main trio. Darkrai is edgy a fuck. Cresselia has an absurd shape similar to lati@s. Wait, there's still more ! Heatran is barely okay (but became obnoxiously omnipresent online), shaymin is useless as fuck (seriously why make it a legendary ?). And I'm sure I still forget a few gen 4 legendaries because there's a fucking ton of them.
>gen 5 legendaries (and gen 5 pokémon overall)
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Gen 6 looks alright for the moment, as long as they stop it now and don't make 30% of the gen's pokémon legendaries.
