I wrote my response quickly, Quillon, so I will go into more detail.
First, sure, a line is a shape, and it can be up-down or side-side in orientation. But I would rather invent more stats and make triangles or squares.
When bonuses are applied to a shape, all of the stats get the bonus. So just like what you said, GREAT-OK-OK becomes LEGENDARY-GOOD-GOOD.
And here's why the shape and its values are better than numbers. In Fallout, stats went from 1 to 10. This makes you think that each number is an increment better or worse than the one after or before. But that wasn't true. A 3 Intelligence is much worse than a 4, compared with how bad a 4 was to a 5, because dumb dialog kicked in at 3. Similarly, a 6 Luck was better than a 5, but a 7 Luck was way better than a 6, because that was the threshold for certain random encounters to become possible. In other words, numbers imply a smooth gradient from low to high, where having 4 or 5 distinct values does not imply that they are linear in any way. They act like thresholds. You expect something new when your Luck goes from OK to Good,a nd from Good to Great, and not just your crit chances to go up a little for each one.
Here's another reason I like shapes better than numbers. Instead of giving you points to spend, and perhaps some additional constraints about not being able to lower too many stats to 1 (because maybe a character with stats of 10 10 1 1 1 1 1 is just not viable), shapes have their constraints built into their geometry. You cannot point all the vertices of a triangle up. And humans have evolved to handle visual comparisons more easily than numerical ones.
I'm not saying this idea of shape-based stats is ground-breaking or revolutionary. It's just a different way of thinking about the issue of character creation and stats. I am sure I would allow an interested player to "look under the hood", so to speak, to see the numbers corresponding to the stats. But many players won't care about that, and most shouldn't have to. It's all part of the "play how you want" philosophy.