Hey all, just wanted to chime in that I'm having freezing problems as well.
I've re-downloaded the game multiple times now, so I've got a fair few scenarios...
1. Game downloads, and I (after waiting four years) am eager to play it. I'm sadly disappointed when I can't even reach the loading screen after the lobby/main menu.
2. Attempts to fix - clear cache, deleted then re-downloaded game. It gets marginally better! I can now get to the first loading screen before the first level. It freezes at 30%. I try this a multitude of times.
3. Attempts to fix - clear cache, delete then re-download game, delete save files, move Xbox 360 to a better position so as to have a slightly better internet condition, as another member Stonculd suggested perhaps it's jittery packets (or something along those lines). Game still freezes at 30%. I am disappointed.
4. Attempts to fix - clear cache, format HD, re-download game, contact Xbox LIVE support. The result - a clean, monitored download, and a game that freezes at the first thing you see (the ubisoft label).
5. Attempts to fix - clear cache, format HD, re-download game, move EVERYTHING onto external storage, use external storage rather than HD for save files. Results - I can play the first level. The second (as you enter the sewers) gets stuck at 30%.
So, personally I'm not sure if this is a hardware or software issue. I don't have any other issues akin to these in any other game (downloadable or not). Xbox LIVE Support referred me to a Ubisoft support number, but the charge is $2.48 per minute (including being on hold!), so I'm not doing that. I've submitted a question 'ticket' and am awaiting a reply. Was simply posting here to make myself known, and if anyone has any other ideas.