Small planet, big pits
At about five hours, and with more collectibles to go if we wanted (but we didn't), Pitfall Planet has a fairly substantial amount of content. The game's simple controls are exercised really well throughout its run, and the stranded-little-robots premise never feels worn out.
Other than the fact that the mouse cursor stays on-screen - there's got to be a "hide cursor" setting they just missed - the whole affair is very well-polished. Even occasional physics quirks, like needing to fiddle with angles to get up some ledges, feel appropriate within the game world.
Pitfall Planet is satisfying and fun, and while it may be a bit on the "mild" side, it's hard to pick out any real flaws with it. (As long as you have exactly two local players.)
Better than: Dyadic, Trine Enchanted Edition
Not as good as: Captain Toad: Treasure Tracker (not co-op, but otherwise thematically similar)
And the soundtrack is cool: stay a while, and listen.
Progress: fixed the spaceship, 89% item collection, got the cat-ears hat