Can I choose between the Bungie Era depiction and the 343industries depiction? And if not, can I choose 'neither'? Because whatever made both the Forerunners and the Flood interesting has long been removed from both factions due to 343i's terrible direction.
The Forerunner of the Bungie era were NOT explained. All you had were these megastructures and fragments of information that allowed you to use your imagination. Not it's just generic 'highly advanced near-humans that were -Yoinks!- and stuck up and got jealous cause daddy chose someone else to be CEO of the family business".
And the Flood, the Flood have always been on that line of boring, but at least with Bungie we didn't get 'space gods that turned into magic space dust and became evil'. You didn't know where it came from, you only knew that the Flood was the most dangerous organism in the ENTIRE galaxy, if not universe.
Before 343i hired people that had no idea what to do with the universe they were given and turned it into the mess we have today, these factions were interesting. Now they're just generic, they are boring, because they were brought out of the shadows and had all their mystery removed.