I love this game, but having to play through PAINFULLY slow levels to finish the campaign TEN TIMES while all you do is hold the fire button and maybe dodge something here and there is just agony...

So if you want to get the Legendary achievement much easily, it's very simple! Just open the console by pressing "~" (tilde button), and type in "veni_vidi_vici" so you can instantly win every level! Do that over and over and the achievement is all yours in no time.