I do agree that Halo 4 lacked story elements from the first trilogy, and how the drastic transition of artwork really had no clear explanation for being there.But from what I know, these issues could be cleared with some novels or even a new plot from Halo 5.
1. For starters, the artwork regarding the Chief and the Warthogs on "Requiem" should never have changed until after he encountered the UNSC Infinity; He could have gotten his upgrades there. And regarding the "Dawn", it should have NEVER changed; its new look would fit right in the futuristic UNSC ships, but the dawn was from 3 years back, making it outdated.
2. Some of the looks for the covenant are better, but their organic structures are off from the traditional covenant. The Jackals look like raptors and the grunts don't look like grunts (Piranha fish faces); the elites are fine. For the Armors of the covenant, a good excuse is found in those 3 years Chief was asleep. Some could simply say that covenant tech. got advanced from those 3 years OR their civil war (still continuing)may have created a shortage of advanced equipment, as Cortana remarked during the mission "Dawn" that the elites were using low grade technology.And for the weapons, you could say that the covenant decided to mimic human weaponry; The UNSC put up a tough fight against the covenant as nobody did before, so they thought to "Improve".
3. Plot holes for the covenant may leave for new ideas for
Halo 5.
The covenant fought in Halo 4; I don't think it's the whole covenant as thought of in the first trilogy. As you all know from Halo 3, the profits betrayed the Elites; killing them throughout the covenant ranks. Such a betrayal from a holy figure will leave many questions and doubts for the victims, the Elites. After the events in Halo 3, there would still be conflict withing the Sanghili Race with those with no faith, and those who were over zealous; the zealous ones were the ones who reunited most of the covenant. IF the majority of the Elites lost faith, then this explains the low tech ordinance the covenant have due to no access to modern Elite Technology. But if most of the Elites found their faith in the new covenant, then perhaps the Arbiter could be a new character for Halo 5 IF he lost his faith. My opinions is that the "Covenant" are a faction of species, not all of them.
As for the Forerunners, if you watched all the Halo Waypoint videos from Halo 4 than you already know the story. The only explanation for the Forerunners I have to offer are the weapons they have, specifically the Light-rifle, Suppreser (excuse my spelling), and the Boltshot; they are similar to human weapons because human weapons are similar to Forerunner weapons. Didact implies during the epilogue that the Humans prospered from Forerunner technology.
Please respond to this post guys? :D
[Edited on 11.21.2012 4:43 PM PST]