The content update I downloaded which included ODST is not working, as it’s asking I purchase ODST when going to the campaign start menu. I’ve lost all faith in 343. I’m not pre ordering Halo 5, and may not buy it at all, as much as that sucks to say, because this WAS my favorite franchise.
The content update didn’t include ODST, it just contained the bug fixes and UI changes to accomodate it. In order to get ODST you need to redeem the code that would have been sent to your Xbox Live account - you can find this in your Xbox One messages or by going to Xbox.com and reading your messages there. One you redeem the code, you can then download ODST. After installation, you’ll find it under the Halo 3 campaign.
In case you missed it, everything was detailed out here in this FAQ blog post. If for any reason you don’t have a message with a code, you’ll probably have to contact Xbox Live Support. Just make sure you’re eligible as per the FAQ I linked. If you are then you can make a post over on this forum