Originally posted by Tzeentch._ I'm not sure why you would want to make this gameplay-centered. In 40K tabletop, terminators can be killed by guardsmen in melee combat. In Dawn of War, it takes dozens of rounds from a tactical marine squad to drop a single model from a Hormagaunt squad.
In any case, gameplay isn't considered canon here because game mechanics take precedence over lore for the sake of balance. Canon descriptions of the sniper rifle outright state that it can punch a hole through a tank. Multiplayer would be unplayable if the gun could actually do that, though.
Spartan armor is impervious to UNSC small-arms fire. Yet Halo MP wouldn't be much fun if everyone was near-invulnerable, would it?
You've made your point, but now that we're going off the lore rather than the game, allow me to do a complete 180 from my previous post and delve a bit further into the workings of the Adeptus Astartes.
Though it is contrary to an earlier point I made to mention, in the lore, Space Marines with a full Geneseed set (the Ultramarine and Dark Angel chapters in particular) do have some immense advantages over spartans. Spartans and Space Marines both get their bones upgraded through ossification of various substances, they both have highly enhanced muscle growth, they both get enhancements to sight and I think there are more physical similarities but I can't think of them.
What Spartans don't have, however, are a menagerie of extra organs that vastly improve their capabilities. First off, a second redundant heart. Not only does it allow Space Marines to survive if they happen to get shot in one of their hearts, but it also boosts blood flow and lets them survive in low-oxygen environments without a helmet. The last bit's not really too much of an improvement, but its still noteworthy. There's also another organ that further enhances the blood's capabilities of carrying oxygen around the body, which allows them to move somewhat faster than a Spartan. To further protect the heart, the enhancements to their skeletal structure also fuses their rib cage together into a single bulletproof shield of interlocked plates. They have another organ that allows wounds to instantly scar over and seal the wound as soon as these "Larraman cells" reach the site of the wound and come into contact with air. In vacuums, however, that might be a problem, I'm not entirely sure.
Then there's another organ that allows Space Marines to operate with no sleep for extended periods of time without suffering from sleep deprivation. It sequentially switches off and on various areas of the brain to simulate sleep on them and allow them to rest without needing the Marine to actually sleep. So they only require 4 hours of sleep at the absolute most, and can operate continuously for maybe two weeks without any sleep at all.
They have an additional stomach chamber which can quarantine poisonous or indigestible food and then neutralize the substance in order to make it safe for the Marine's normal stomach to take in. And then there's another organ that allows Space Marines to absorb the genetic material of whatever creature they eat. The organ then converts this into a set of memories and experiences that the Marine can then use to understand more about the environment and what the creature had been doing prior to its death. It improves their odds of survival on unknown worlds, essentially, though they're pretty well off even without it.
Then there's an additional lung that allows them to breathe in low-oxygen or poisoned atmospheres, as well as underwater. When this second lung set is activated, the normal lungs are closed off to prevent the aforementioned hazards from getting inside. Then their ears get replaced by a newer, superior but otherwise visually identical ear system which makes them immune to dizziness or motion sickness and allows them to filter out or enhance certain sounds.
Then there's an organ that allows space marines to undergo a state of suspended animation either consciously or in response to extreme bodily injury. They can survive in this suspended animation for years; one space marine was recorded to live for over 560 years in that state before being revived. The down side, however, is that they can't turn it off on their own, only chemical therapy or certain other methods can wake them up.
Then they get an organ which allows their sweat glands to secrete a substance that coats their entire bodies and tints their skin to survive high levels of UV radiation, also protecting against other types of radiation as well. Then there's a second kidney that allows them to filter their blood much faster than by default, rendering them immune to most poisons, at the cost of going unconscious in order to circulate the blood through the second kidney fast enough to rid it of the poison.
And then there's an organ that, like the one which darkens the skin, coats the skin in a substance that seals it up and gives it resistance to extreme heat and cold and even complete vacuums. Then there's another organ that enhances a Marine's sense of taste to allow him to identify most common chemicals and even track targets through taste.
They get another implant that allows them to directly interface with their power armor, but Spartans have that too. Still, its noteworthy due to the fact this implant is put directly beneath the skin of the torso in multiple sheets. It then hardens and, after a maturation period, has holes cut into its surface for various neural sensors and interface points to be fitted and used by the Marine's body.
The last organ they get (besides one more that is required to grow the rest, but is eventually harvested to be used in other marines) is a fun one. Its a set of glands in the lower lip that allows them to spit a highly corrosive and extremely deadly poison that can burn through metal if its given enough time. Note that almost all of these organ advantages I've listed are protections the space marines have when they are wearing no armor whatsoever.
And going onto the training of a Space Marine versus a Spartan, even though Spartans start training from age 6 and Space Marines start from 16-18, the Space Marines are usually recruited from the most unforgiving planets possible. Death worlds and Feral worlds are the preferred types of recruitment planets, as anyone who can survive in such conditions is already someone to be reckoned with; further refinement through high risk training only makes them even more formidable.
Besides the initial live experience, Space Marines train for combat four times a day (two practice battles and two firing exercises) every single day when they're not out on a mission. Not only that, but the only meal they're usually allowed to eat is what they kill during the first battle practice of the day. If they can't kill, they don't eat.
Then there's the issue of enemies: the worst thing that a Spartan has ever faced is the Flood, excluding those Prometheans from Halo 4 (Again, have not played it; I've no right to talk about it), which was a hive-mind-based parasite that could overtake any creature of sufficient biomass. They could learn from the memories of their hosts and use any bit of technology those hosts knew how to use. In addition to them, their common enemy throughout the series has always been the Covenant, an empire of religious zealots made up of a diverse group of many various alien races. However, the Covenant are truly just one army, rather than each individual race being counted as one.
However, the Space Marines regularly do battle with the Eldar, the Orks, the Tau Empire, the various forces of Chaos, the Necrons, the Dark Eldar and the Tyranids. All of these races individually vastly outgun and outman the Covenant, and then the Tyranids outgun and outman the Flood sheerly through bio-diversity and the immense scale of their race.
I'm not going to go into detail explaining each one of the mentioned races for the benefit of anyone on here that doesn't know them, but considering the Space Marines can hold their own against all of those incredibly dangerous enemies and that Master Chief is basically the only surviving Spartan left as of Halo 3, there is a big difference in the level of expertise between the two forces. Master Chief is the most exceptional Spartan in existence, but I'd say he's about on level with a veteran Space Marine, but against really high ranking ones, he'd probably have a bit more trouble against them due to how much more experience they have over a standard vet.
That's not even to mention the Adeptus Custodes, the Emperor's bodyguards (literally, lol) who could kick even the greatest Space Marine's ass if it ever came to that, or the Primarchs, who could in turn kick the asses of the greatest members of the Adeptus Custodes. All I'm talking about here are the regular Space Marines, and regardless of what anyone would like to think, they are extremely formidable.
I'd go into MJOLNIR armor and its permutations vs the various iterations of Space Marine armor, and maybe Halo weapons vs 40k weapons, but I've almost hit the character limit with this colossal post and don't want to start and end up running out of space.
Anywho, I'm not by any means a total expert on everything there is to know about the Spartans, but from what I did retain from the Halo lore and what I now know about 40k lore, I am pretty damned sure that Space Marines very much out-soldier most Spartans what with everything I've written above. But regardless of any replies that I get, I'm probably not going to reply back; having so few posts on this forum, I don't enjoy the fact that only one of them is on-topic to the thread. Its a pet-peeve of mine; unless there's something I absolutely need to respond to, this is going to be my last off-topic post for a while.
So I guess that's all. Sorry for the giant post. :<