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Ultramarines provides examples of the following tropes:
All There in the Manual: The prequel comic that comes with the Collector's Edition DVD explains the situation on Algol: why Proteus complains about the lack of glory there, why the Ultramarines can only spare a single squad to go investigate the situation on Mithron, and what happened to the original Ultima Squad.
Anyone Can Die: By the end of the movie, everyone with a name is dead except Proteus and Verenor, and maybe Nidon.
Bottomless Magazines: A bolter magazine holds 30 rounds, and less than that for the pistols. The squad is firing on full-auto most of the time. Rarely will you see anyone reload, and no one ever runs out of ammo.
Also, the Black Legion are trying to fire at full sprint, while Ultima squad are either standing still or slowly falling back.
Ultima squad too during several other firefights, but this is actually something of a case of Reality Is Unrealistic. Depending on environmental and situational factors, for every casualty inflicted a Real Life military force can expect to lay out one to three thousand rounds, most of which is suppression or covering fire (which the Marines yell for at least once or twice) which is basic spray-and-pray to just get the enemy to keep their heads down.
Recycled Script: The story of the movie bears a couple of similarities to Gordon Rennie's old Bloodquest graphic novel: it has a squad of Space Marines (including a young recruit named Proteus) going on a dangerous mission involving a sacred artifact and losing their Captain to daemonic possession. At least this Proteus doesn't fall to Chaos.
Running Gag: "The Emperor protects...but it doesn't hurt to have [insert useful, common-sense piece of battlefield kit here] either."
Pythol is clearly the oldest of the Marines, and is also the most cautious, the least interested in glory, and the most cynical about their chances.
Brother Nidon of the Imperial Fists is the one in charge of protecting the shrine's relic. The task has clearly taken its toll on his emotional state, and seeing 98 of his Battle Brothers get slaughtered can't have helped matters. Turns out he's no heretic, though.
According to the prequel comic, Sergeant Crastor also qualifies, being the Sole Survivor of the original Ultima Squad. We don't really see enough of him in the movie for this characterization to shine through, though.
The Smurfette Principle: There is literally one female character in the entire story, and she doesn't even show up in the film itself, only in the prequel comic. Justified in that this is a story entirely about Space Marines, and Space Marines are a One-Gender Race.
Tranquil Fury: Severus when Ultima Squad prepares to keep going after the killing field where Guardsmen and a few Imperial Fists lie massacred.
"That beacon may lead us to someone who can... explain."
Unwitting Pawn: Proteus. As the daemon points out, it only got as far as it did with Proteus's help.
What Happened to the Mouse?: So... are they just going to leave the Land Speeder there? Aren't those things expensive? And what happened to Nidon after he was knocked unconscious during the final battle?
Assuming Nidon survived, he likely would've been transferred back to the Imperial Fists. Probably with a few battle-honours earned, considering he helped put down a daemon.