Ullström has a combination of skills that makes him an intriguing prospect. First and foremost, he has very good size and strength. He is big and uses this to his advantage in most situations. What makes him stand out is that he is a really good skater for a player of his size and reaches very good speed. To go with his speed and strength, he has above average technical skills and stickhandles very smoothly through traffic. His coast-to-coast rushes were a trade mark of his in the Swedish juniors.
Offensively, Ullström is a natural good scorer that rather finishes a play than delivers the puck. He has a good shot, a quick wrister with good accuracy. He is also aggressive and usually has a few good hits per game. There is little to complain about when it comes to Ullström's offensive game. Defensively, however, he does not play it as safe. He back-checks, although perhaps not as effectively as desired and sometimes makes too risky plays in his own end. Also, consistency has been somewhat an issue, as he has been known to be streaky.