Leonidas tells the traitor Ephialtes to live a long life. At first, it seems that Leonidas is telling him "Good luck with your life," a moment later Ephialtes breaks down in tears. Why? He was trying to regain his father's spartan honor, and in Sparta, you were only respected if you fought and died in battle.
He's also telling Ephialtes that his name will go down in history as a traitor, much the same as Benedict Arnold in the United States or Vidkun Quisling in Europe.
He's also completely and utterly disowning Ephialtes as a Spartan. The hunchback only wished to be proven worthy as a Spartan, and his king has essentially denied him this. Forever.
In the beginning, Leonidas lures a wolf into a tight passage and spears it, because the wolf was basically trapped and helpless — he uses the same tactic during the battle of Thermopylae: he lures the huge Persian army into a small space where they can't make full use of their vast numbers, and can only send smaller forces, which get massacred.
Quite possibly accidental Fridge Brilliance: Gerard Butler's frequent accent slippage actually puts his characterization of Leonidas in line with a long-standing Translation Convention. Spartans were often characterized as having Scottish accents when Ancient Greek plays were translated into English, drawing a parallel between how the English and the Scots regarded each other and how the Athenians and the Spartans regarded each other: prissy intellectuals versus short-tempered bumpkins.
Another case of Fridge Brilliance: The movie and the comic aren't regarded as very accurate in terms of historical events but rather a take on actual events put into a medium that makes for a fantastic story. At the end of the film the events are being told to Greek troops to hype them up for the approaching battle. The entire premise of the movie and the comic it was based on amounts to wartime propaganda to raise the morale of the home team!
The almost complete lack of fantastical elements in Rise of an Empire, which takes place before, during, and after the events of this film, gives more evidence to this.
Yet more Fridge Brilliance: Although the fighting was heavily stylized to the point of absurdity, when reading Greek literature such as The Iliad, one notices that the plot essentially stops for pages upon pages of gory descriptive combat. While the film may not be an accurate representation of Greek history, it does an amazingly good job of emulating the tone of Greek Epics.
Similarly, as Kyle Kallgren of Brows Held High famously pointed out, the ancient Greeks probably didn't have a word for blue, with Homer describing the sea as "wine-dark" and the sky as "bronze." Hence, the film's infamously stylized color pallet, with yellow skies, dark purple seas, and almost no blue anywhere.
On the subject of combat: Yes, the phalanx formation falls apart almost instantly in favor of stylized melee. But look at how Leonidas and the rest of the Spartans are fighting in that melee — they're not killing or finishing all of the soldiers they run into as they charge. Many are instead left stunned or knocked over for the Spartans behind them to finish off. They might not be in the tightly-packed phalanx, but they're still fighting as a unit and trusting their fellow soldiers to protect their backs and flanks as they advance.
The idea of Dilios making up details for the sake of rousing up the troops may have been true. During Leonidas' training, Dilios said that he was taught to show no pain... right as he is showing a pained expression as he is getting beaten.
Another point to Dilios making up stuff. The absurdity of the "creatures" in the film itself can all be attributed to Dilios' storytelling, making 10 foot Rhinos, Giants, God-Kings, Immortals, etc. He is using hyperbole to rouse his men to a glorious fight with tales of the 300.
When the Persian ambassador asks for earth and water, this is actually a backhanded and realistic request for citizenship. Only Citizens of Sparta were allowed to own land in Sparta, so by asking for land, the Persian was asking to become a Citizen (and also a voting member in the council).
One small omitted detail was that the Thespians and Thebans remained at the battle, while Dilios depicted the rest of them running in the tale. While this sounds like a dick move on Dilios's part, it actually makes sense since he wasn't at the battle and still hasn't seen the corpses on the battlefield, so he was going on assumption. Furthermore, since the Spartans themselves thought it was brave of the Thespians and Thebans remaining to fight, it explains why Dilios didn't even consider the possibility of the non-Spartan forces remaining.
The Persians didn't believe that their King was a god- however the Greeks believed that the honors bestowed upon him- particularly proskynesis (An act of kneeling that was expected of all Persians to perform before their social betters) were only worthy of deities, and thus it is logical that Dillios would believe the Persians worship their king. There's also the fact that at this stage Zoroastrianism wasn't the state religion of the Persian Empire, so it's possible that some Persians did believe their king was in some way divine- though it's doubtful Xerxes himself would believe this.
The Spartans using the corpses of the Persian scouts they slew to build the wall at Thermopylae. While it's an example of the Spartans being both practical with "human resources" and using it as psychological warfare, there is another purpose to it, as well. Earlier, the Spartans and their allies had encountered the Tree of Death, a tree to which numerous civilians had been nailed to, with only one young survivor to tell them what had happened. The men who had done this? The aforementioned Persian scouts. So the Spartans killing them and using their bodies as mortar for the wall was also a case of payback.
When we see a close-up of Leonidas' corpse, we see arrows puncturing every point of his body except his head.
Combined with Easy Logistics: Each of 300 Spartans only bring cape, loincloth, spear, shield, and some helm in them. There's no mention of incoming and delivering foods, tents, or blankets to them. Yet, they fight for more than a week with high spirits. The only possible explanation is Dilios omitted them from his propaganda work for Home Team. Then, who sent the food if it's actually delivered? Because, you know, the Spartan Senators back home didn't agree with war thing.
First of all, historically, armies tended to maintain their food source from foraging the land and pillaging human settlements. Even for well-organized, sophisticated military forces such as the Romans and the Qin Chinese, an actual logistics was the exception, not the norm, and even when a logistics system was in place, food tended to be down the list of delivered goods. Pre-Napoleonic logistics focused mainly on getting equipment and weapons to a place. Considering the Spartans were already shown as training to be hunters, finding food at Thermopylae shouldn't be a problem. They just didn't show such boring bits onscreen. Secondly, the Spartans were not the only soldiers in the battle. Other Greek city states (some who are either too pampered to give up luxuries even in war or were more sophisticated than the Spartans outside of war) such as the Athenians were in the battle. So, it's safe to assume the other Greeks were supplying Spartans with supplies. Also, they fought for 3 days, not a week, and this Spartan unit was not a regular Spartan unit, it was the King's ELITE BODYGUARDS (which in real life would have been some of the most battle-hardened veterans and been trained far beyond the regular Spartans in things such as assassination attempts on generals, etc). Without a doubt, they'd have already fought in campaigns where food shortages happened and they would've been the equivalent of special forces in battle (who can fight non-stop for entire days, even weeks, without sleep and food assuming they are resupplied with ammo and water and they have backup support or some other ridiculous advantage such as terrain, etc).
Ephialtes is heavily deformed, but not only does he show himself to be fiercely loyal to Leonidas despite his parents' self-imposed exile due to Sparta's policy of killing anything less then perfectly healthy babies, he also shows that his spear-thrusts may as well be coming from a post-driver, and also that he has an intimate knowledge of the surrounding landscape that could prove vital to the success or failure of Leonidas' plan. All that he asks of Leonidas is a chance to fight with the Spartans to earn his father's helm and shield, and validate his parents' faith in him...and Leonidas turns him down, telling him instead to pile up bodies, tend to the wounded, and fetch them water, which he visibly already has his own warriors doing. Leonidas justifies this because Ephialtes' deformity means that he can't lift his shield very high, which would admittedly weaken a phalanx...but the Spartans are rarely ever all arrayed in a phalanx, and the narrator already snidely refers to the supplementary Arcadian force as "more brawlers than warriors [and] brave amateurs [who] do their part," so why couldn't Ephialtes be included in the defense force? If nothing else, why on Earth did Leonidas just turn him loose after trampling literally the only thing he wanted out of life?