Space marines are massive super humans, who undergo about a centuroy of training, and recieve a series of implants and stuff. Your typical space marine is IIRC, about nine feet tall with two hearts incase one gets shot, and can crush a human skull to dust with one hand. His bones are laced with ceramics from his diet, his spit is acid that can eat through metal, and he's just a general all around badass.
Encased in their ceramite power armour, spays muhreens have some recawkulous feats. Among them:
-Ripping the hatch off from a Lemen Russ. To put this in perspective, the Lemen Russ is a battle tank from the future designed to shrug off damage that would slag a modern tank. Lasguns, often called "flashlights" in 40k because of their general impotency, have no effect whatsoever on a tank like this, or space marine armour, for that matter, leaving just a black spot in the paint. A lasgun was confirmed in Imperial Armour to have a 70 megawatt output. A single shot from one of these would lulz entirely at a tank. Lasbolts have punched through three solid feet of concrete, which from a physics stand point is actually kind of insane given that they're laser weapons. Space marines are strong enough with their armour to rip the hatch from one of these. Not necessarily break through it's armour, but impressive none the less.
-Lifting and carrying large vehicles. (like.. say, a semi.) Another good strength feat, achievable by any man in power armour, easy for a marine. Hell, in on of the Ciaphas Cain novels Inquisitor Amberly does this with smaller less powerful armour. Abaddon, obviously NOT your typical marine, once lifted an entire baneblade (massive tank covered in lascannons, weapons which are just plain stupid) with one hand and crushed it. But yeah, I just wanted to mention it because Abaddon is a badass.
-Their armour, as I already mention, shrugs off lasgun fire, as well as monomolecular edged melee weapons. It takes the strength of another marine to penetrate the ceramite plates (which are about 5mm thick, IIRC, but might be wrong), with a monomolecular chainsword or axe to pierce it, and even then, the armour is still effective.
-Their combat speed and reaction time are super human to some extent, but I have to look that up. I forget exactly by how much.
-Their weapons are basicly "what's the most badass thing ever? And how do we turn it up to 11?" incarnate. I do not exaggerate when I say space marine weapons can include:
Giant, monomolecular edged, chainsaw swords ON FIRE.
Fully automatic, rapid fire, armour piercing, 1.00 calibre rocket propelled grenade launchers on 'roids. (Bolters. Standard weapon. 😐) Bolter rounds are supposed to be hypersonic, but I can't supply the source on that. It might be a codex, but I don't have the space marine codices handy atm. Will look around, and stuff. But yeah.
Those are the two standard issue weapons 3 of the 6 marines presented have. haermm The Librarian has what amounts to a +10 vorpal sword of psychic awesome (a force sword). The heavy bolter carried by the final marine is like the other one turned up to 12. (Bolters are already 11!) with a much larger magazine size, larger more powerful rounds, fired more rapidly, effective over a longer distance (so probably faster, too). Yeah. Things.
Also, the round fired by a bolt gun explodes in it's target, hence the grenade launcher thing. Consider that bolt guns are effective against other spays muhreens to some extent, and you can imagine how strong they are. 😐