These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
The same goes for Odysseus, who is presented in the Aeneid as more of a slimy trickster than a hero.
The most difficult one is Helen. In one scene, she's suffering a total breakdown. In another, she's gleefully killing Trojans. It's possible to reconcile the two, but there's such a disparity that it may be one of the incomplete parts (see below).
Author's Saving Throw: Virgil justifies the Trojans falling for the Trojan Horse so that they wouldn't go into the story looking like moronic losers, complete with the Trojan who vociferously argues against it, to the point of attacking the horse but whom the gods then strike down (along with his two children).note Elements of this go as far back as the lost Sack of Ilion, though there the death of Laocoon occurred after the Trojans decided to bring the Trojan Horse into the city, and his death was the portent that caused Aeneas to leave Troy with his companions. Virgil also stresses the fact that they kept Troy safe for over a decade and only lost by underhanded trickery.
Nintendo Hard: Translating it, especially for students that have just come off prose. Vergil's poetic endings, word order (or lack thereof), and figurative language can be quite annoying. Author Existence Failure also leads to some incomplete lines, making translation even more difficult.
The phrase "The Arms and The Man" (the title of a Shaw play) is from the first sentence of the epic and the memorable line translated as something like "going to hell is easy; it's getting back which is the hard part" might be considered the origin of the phrase To Hell and Back.
There's also Vergil's description of Dido re-discovering love as re-kindling "an old flame." (Though the 'flame' is her sexual feelings more generally rather than a passion for a specific former lover, as it is usually used in English.)
"We each have our own demons to face" is from the sixth book, though it's far more literal than most modern uses: it's literally about being punished for one's sins in the underworld.
The Woobie: Aeneas. When he's introduced, he's bawling his eyes out over the threat of immediate death by drowning. He gets more pathetic from there, possibly changing once he gets to Italy.
Dido is also portrayed quite sympathetically. Turnus skirts this during the parts when Virgil describes how he is doomed to die, and when one remembers that he didn't initially want the war at all and only got involved because of Juno and Allecto's manipulations.