I'll check it out. Never really thought about the politics within the universe but the series does have its plot holes in that regard.
Correct me if I'm wrong but doesn't slip space work off the idea of "bending" the universe around it as opposed to actually going faster than light? Could've sworn that was a real concept. Like you said FTL isn't really possible due to the complications it raises
. What about things such as hard light and how the Spartan program would work (politics aside)? A lot of the tech they have seems plausible.
The slipspace is basically hyperspace of Star Wars, in practice. Halo's technobabble paints it as a dimension that is "bent" and offers short-cuts that way, more so than actually allowing faster travel in conventional way.
As for hard light... there is a theory that light can act as a solid. But apparently this is related to computers, information and such, not something that allows forming light bridges and stuff.
And as for super soldiers... Perhaps it is possible that one could train ideal soldier by training them since they're a child. Perhaps not. Yet that doesn't mean they would be that much more effective soldiers, even with fancy equipment. Commandos have their uses but they may not be very cost effective necessarily. Special forces cannot win wars really. It is questionable whether a soldier who has trained since childhood would be more effective than a modern special forces soldier.
The Mjolnir itself is pretty much technobabble, though its predecessors are much more realistic powered exo-skeletons. But equipment doesn't make one a soldier. Solve the issues relating to powered exoskeletons and equip special forces with them and you essentially gain science fiction's super soldiers, yet they still don't win wars alone. And Halo's Mjolnir is described as terrible cost-ineffective. They equipped perhaps some 30-40 people with the armor, and they could have gained a big fleet of ships for that price.
Especially silly since you could have put AIs in those armors and they'd be far more efficient than humans, no human can ever beat a computer when it comes to reflexes, provide the computer is programmed correctly and has working sensors (basically the same requirements humans have...).
As for the bio-chemical augmentations... Well, we can't make such. Yet. They are also portrayed as cost-ineffective, at first. Honestly, such things effect is part of transhumanism, and it has bigger cultural and socio-economic implications.
I reckon i could go on and on about these, and more in-detail.
EDIT regarding the UNSC politics and culture and such. One big issue is that of time. 500 years in the future yet the culture is very similar to ours? How odd. 500 years ago the world was very different. And then there's the issue with the economics of space travel. And other things. Like how the hell does single government control a big amount of human colonies, and how come most are okay with it? If it were described as a confederation, a coalition it would make more sense, especially given the slowness of human FTL travel (taking weeks or months). And this relates to the Spartan Program. There's going to be a rebellion... so force everyone to stay. What. Even with super soldiers... that doesn't make any sense. Why not grant the outer colonies independence and form a frigging coalition or such?
Of course, no one has really fleshed out the pre-war UNSC... these issues can be explained.