For the most part, he achieves his objectives. Sow as much destruction and anarchy throughout the Imperium while picking up some cool toys to kill stuff with. Horus was direct but overconfident. Going straight for Terra was a huge gamble that ultimately cost him the war. Abaddon is playing the long game, though, to his mind, he isn't a servant of the Dark Gods but using them to further his own agenda. Bare in mind that he is quite mad
lol.