Machine sushi rice tends to be packed together, and I think it's usually cooked a little firmer so that it survives machine handling. There's a finesse that good sushi chefs have that hasn't been replicated by a robot yet.

Good sushi rice is somehow lighter, but still cohesive. The flavor balance with the fish is better and more consistent. The fish doesn't tend to fall off as easily.

If you eat a fair amount of sushi, you'll notice the difference. If you don't often? Maybe not.