Most Force users never display the kind of telekinetic feats he produced. He tore his capital ships from the grip of the mass shadow superweapon on Malachor V, and then held it in one piece. Not only was that an extremely impressive scale feat, but also one of endurance.
However, Drain was his big thing, mostly because it was controlling him. He could devour entire worlds with it, like the Sith Emperor, only much faster and without the need for rituals. In fact, it was stated to be more a product of instinct than technique. He even naturally drains any beings around him, mentally and through the Force, and was so corrupted by the Dark Side that his natural speech caused agony to anyone that heard it.
The problem with Nihilus is this; minimized exposure and lore-centric. He wasn't paraded through the game like Sion, or even Malak from the first game. Because the game was rushed for a Christmas release, much of Nihilus' scenes were cut. A good example is the restored Sion vs Nihilus clip that can be found on YouTube, where Nihilus casts some explosive Force attack.
With scenes like that gone, he was just this figure existing for the sake of existing. Just gameplay elements, which is never ideal to go on. However it is very clear from several characters, like Kreia, Visas and even Tobin, that Nihilus was both designed and intended to have been, lore wise, inhumanely powerful. Like, literally, his humanity and human perspective was extinguished.
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