When you buy a game it must meet standards our the game should not be launched and when bugs arrive their is an agreement that they will be fixed by the game developer.
Halo CE CO-OP is not working for most users over Xbox live now if the case is with Xbox live then the game developer has the right to do nothing about it because Xbox live is not their service but we know and the game developer know that Xbox live is not the problem and it reverts to the game having a problem.
By Law when you buy any piece of software it must meet the requirements in a document that would be sent to the game developer to crate and it must meet those requirements where necessary and the buyer should expect those requirements to work by default at an appropriate standard.
Now Halo CE CO-OP may work but it is not working at an appropriate standard by experiencing major lag/fraim rate issues when playing over Xbox live.
In my opinion and the evidence I have collected the game should be fixed by a necessary patch to meet the appropriate standards for CO-OP play over Xbox live and the necessary approach should be on going right now or at least a plan to take an approach to the problem as the fault has been there for sometime and still no solution or approach to fix the problem.