I wouldn't call it underrated. It seems to be very popular and often has better ratings than other very popular games. Personally I think it's not necessarily bad but slightly overrated. I would've liked to try the more detailed designs in a more complex, less fast paced/arcade-y version of the game.
Interesting, the early designs remind me a lot of the interiors in Wayward Terran Frontier. Especially "The original sketch of the Kestrel." in the upper right.
