In seven pages I haven't seen what makes the W40k Space Marines awesome for me. The process of becoming a brother of the Chapter.
I mean, those in said chapter go on their base planet, or another, depending on again said chapter, select certain outstanding warriors, teach them about the Emperor, modifies them genetically and puts them through tremendous amounts of surgery, most of which hurts like hell and kills most, get another heart, a special lung, another organ that makes their bones ceramic and their ribcage a solid bulletproof plate, a sub-skin interface to their incredible power armor, acid spit glands that makes them able of digesting paper, eye implants to see as well at night-time, another organ to neutralize every known poison, some neural implants and another organ that bolsters their muscles a damn whole lot?
In this period they barely become Initiates, the scouts of the Space Marine army. Even so, an extremely small part of those that are put through these modifications actually survive them. Many simply mutate into madness and have to be euthanized or killed by the Initiate performing his own Trials of Fire which differ from chapter to chapter. Most involve putting these initiates in active combat in the 10th company of the chapter.
They aren't as well armored as their Space Marine brothers, but they are still bad-ass. After completing these trials the initiate finally attains the rank of a Space Marine and is given is oh so awesome power armor. While the armor does bolster the strength and speed of the marine, the guy under it is trained well enough and most likely hundreds of years old, veteran of many battles. Their equipment is more than tools they use, they maintain it religiously.
Now then, the space marines kill so many types of alien, mutants and heretics that it makes their own gloves bleed, yet even so, losing bits of them and tons of modified blood, they maintain their bad-assery.
I can see why the Master Chief is a dumbed down version of Space Marine. He is well trained, but so are Green Berets. He does fight a lot of aliens, but I could see no drop of red blood from them. Also I doubt I'd ever see him standing in front of an army of green-skinned orks howling WAAAGH or teleporting eldar firing shurikens, necrons or worst of all, tyranids... Besides there are some space marines so badass they don't even wear their helmets anymore (although having them on is much more stylish

).
Note: Bolter fire is .75 cal (1 cal for the heavy bolter) and as long as a knife. It uses rocket propellant and is high explosive (the normal bolt that is, there are many types). Because of being as large as a fist and high explosive, this WILL blow you up

. Also, the bolter does not produce a lot of recoil when fired because of being rocket-propelled (it's more akin to an RPG then a normal AK47).
I don't know about the Starship Troopers guys - I know that they were salughtered wimps in the movies, but have only heard awesome things about the novels. Might read them someday.
I don't see why the Marines in Starcraft are seen as wimps by you guys. Sure they do die easily in the game, but they can only do so much. The one inside is only given basic training before being thrown into the fray, and despite seeming weak, they are actually quite well-equipped. Their gauss rifles is nowhere near the bolters of the W40k guns, but the technology is much lower as well. The armor is bionically enhanced and quite awesome, but when against enemies like zerg that have acid spit capable of going through steel or protoss that can phase you out of existence, you really don't have much choice but fire or/and die.
Someone said that the technology of W40k is much lower than that of Halo. It's not... really! Plasma guns are quite common in both universes, but while the Mjolnir armor is bionical and heavy, the power-armor is custom tailored for that certain marine and connected both neurally and physically via black-carapace. And Halo still has pistols firing bullets... that's so 20th and 21st century!
Hope you liked my ranting.