Intuitively, I think similarly--and then I put two pieces of the same text next to each other, one in Helvetica and one in Roboto, and I immediately sense a subtle difference in personality that I can't put my finger on but I know is there.
Roboto has slightly looser strokes and shorter tails than Helvetica, but their letter shapes are very close. Here is a diagram showing Roboto overlaying Helvetica:
