As anyone knows who has played the new Flood mode that 343 industries has brought in to replace infection, it is awesome. Perhaps the pistol could be buffed so you can actually use it against them and only require one head shot, and perhaps the Uber-thruster pack they seem to have got their tentacles on needs to be nerfed; yet overall the experience is incredibly fun.
The problem comes due to the fact that if somebody wants to recreate one of the many classic examples of innovation and ingenuity from Halo 3 and Reach like Writer's Mind, Smear the Quear, Ghost Busters, Trash Compactor etc. then they need the ability to give the zombies weapons, which cannot be done in the new Flood mode.
However, that is really only the most glaring issue for potential game creators because in many fun and enjoyable new game modes infection is only used because it allows one team to "convert" the other and in the context of the new game modes it makes much more sense if both teams remain humanoid; take Ghostbusters for instance, where it is actually the humans infecting the ghosts which would not make any sense if, when the ghost is killed, it turns into a decomposing heap of very bouncy tentacles. This is irrelevant anyway because the "Flood" gametype would not allow the in-game "zombies" to be given any weapons.
To remedy this I can think of a couple of quick and fairly easy (I think) solutions to implement in one of the frequent title updates that you said you would be doing:
Firstly; you could create a separate gamemode from the "Flood" mode called infection and with all the tools (and maybe more if you can think of them) gamers would require to make games as awesome, if not better, than there were in previous games.
Secondly; you could make the Flood game types a sub-mode of infection so that the character models of those who have been infected can be changed, perhaps from flood to Spartans of a certain colour and/or maybe new models that could be used for other great new games.
Thanks for reading this everybody,
and to any 343 employees who may be reading this,
please do something to allow the creation of inventive new game modes that would use infection as a base, and then once you have done that please go around and put back in everything crucial to the continued thriving of the Halo Community, such as something as simple as Randoms that you took out from Halo 3 and Reach.