I've been using Abaddon more as my group plays higher-point games, and he is yet to disappoint. Yes, he usually slaps his face with his sword at least once a man, but even a roll of 3 extra attacks usually means he'll pulverize his target. Non-EW HQs with T4 get pulverized on the first save they miss, and with his Eldar-worthy Initiative, that usually means they don't get to hit back.
Against other heavyweights, It's a bit of a crap shoot. Logan, Mephiston, the Swarmlord and Calgar are just as strong and usually have better defenses, but don't have his volume of attacks. On the other side, they very often do a lot more to help their armies via strategic rules than Abbie.
Recently, I've been splitting him a lot from his unit in objective games and sitting him on the enemy home objective. His 4 wounds, EW and T5 mean it can take a lot to kill him, making the eney divert a lot of fire from your other troops to remove him. In my last game, he stood for 2 turns contesting a Salamander objective by himself, with half of the enemy army pelting him with twin-linked meltas, flamers, bolters and assault cannons, and he only took 2 wounds (from the bolters).
But assault MeQ's, tactical terminators, Nob bikers, Nobs and other stuff with low-to-average Inv saves with him and 5 times out of 6 he'll make you proud.