There are two really impressive things about this piece. The first is how Aldiss unfolds the story. We know all along that we are inside a starship but Aldiss keeps the plot exciting and provides a good drip-drip of suspense and revelations. The ending also provides a nice surprise and a good resolution. The second impressive thing is that this is a page turner. Some SF provides enjoyment by allowing us to bathe in the details. Not here. We want to find out what happens.
The atmosphere and the characters instantly print upon the mind and the feel of the ship as the characters make their winding trek through the decks filled ponics (overgrown hydroponic plants) is perfect. One fault means I can't give a perfect score. One of the main groups of enemies are rats. This is perfectly acceptable as a plot device (it drives the tribe of Gregg into teaming up with forwards and allows the laser and the diary to be passed on) but did the rats really have to be telepathic?! Did they really have to be able to wield objects and subjugate other animals like rabbits and moths?! Rats on earth have not evolved such abilities. Another fault is that Complain never gets to meet up with his old tribe. We never get a moment where they see how he was right to question the nature of things.
All in all I think this work will stay in my mind for a good long time.