4. The Flood
Since their supposed defeat in Halo 3, the Flood never made a comeback in Halo 4, unlike the more stubborn alien 'Covenant' army. While it would be unwise of them to remove the classic alien foes, it would be appreciated by many fans if the Flood were to be written back into the plot. Even if they did not play such a significant role, fighting a few groups of stragglers would complement a darker tone - should one be incorporated - and allow for horror-style gameplay to add to level variety. Dismemberment of Flood enemies could be a tactical feature - as seen in the 'Dead Space' series - and the 'immersive' melee sequences mentioned earlier could even play a role, perhaps a 'parasite form' could jump at the player's helmet whilst their shields are down. Whatever the case, the Flood seem to be a much loved and sorely missed foe, their significant others - the Forerunners - appearing to be less favoured, likely due to their bland colour schemes and irritating mechanics. On the topic of hostile AI, it is clear that Forerunner enemies will be something we see in Halo 5, so the developers should make strong efforts to ensure that they are entertaining adversaries. Whilst in Halo 4 the Forerunners reacted well to one another - using various powers to interact during battle and strengthen their fellow soldiers - there were too few enemy types and more 'special' abilities could have been attributed to them. Also, the incorporation of indigenous aliens that are unique to whatever planet the protagonist is on - something that Halo: Reach touched upon - should also be something to consider. The huge pair of animalistic aliens found on Reach were a fun and surprising addition, so the inclusion of some new and more frequently seen 'wild' aliens would be a refreshing change to the normal foes that we faced.