Altogether now: "whaaaaat."
I mean, I suppose a package of 30 games, including a fair few from last-gen, could be expected to be big - but when it's 10% of your entire hard drive, that suddenly seems like quite an investment.
In fact, it's those Xbox 360 games that are causing the problem. An Xbox store listing explains that the game itself comes in at 11.26GB, but that the 360 games aren't actually on-disk. As the listing puts it:
"After purchase, the Xbox 360 titles within Rare Replay will also be added to your download queue. Installation space for all titles will require a further 38Gb. If you cancel the installation of a title, you can reinstall at any time by locating the title in the "Ready to Install" section of My Games & app or within the Xbox Store."
At least that means we can pick and choose which games we want downloaded, instead of forcing the entire download on our poor, beleaguered HDDs. The game arrives on August 4th - ready yourself.