1. They're actually acknowledging and dealing with the consequences of the past 8 years of MCU battles
After 8 years of blockbuster battles, the MCU is (very organically) at a point where people might start to think "Hey - these superheroes are bringing some massive disasters along with them every year or so." It's such a simple, logical thing, but one that very few franchises actually take the time to acknowledge (although it seems like Batman v. Superman will be tackling the massive battle at the end of Man of Steel in a similar manner, but that might be more in response the outcry over Superman's disregard for casualties in that movie).
Also interesting - not too many people actually died in any of these battles. Like, an entire city was decimated by robots and lifted into the stratosphere and dropped and exploded and less than 200 people died?! The Avengers did an even better job evacuating the city than I'd realized.
2. They're finally introducing The Raft
Up until this point, where would you keep villains who were captured in Marvel movies? Especially superpowered ones? There really wasn't an option (except for Loki, who got held in Asgard's equivalent of Hannibal Lecter's glass cell), but the movies wrote this off by having the vast majority of their villains killed or disappeared (like Red Skull). Now, there's finally an option: the Raft, a prison for superpowered criminals.
3. There might actually be CONSEQUENCES for the heroes!
The Civil War comics storyline is pretty famous (or infamous) for temporarily killing off Captain America and causing massive divisions in the Marvel-616 universe for years to come, and supposedly the film Civil War will have similar consequences for the overal MCU (although thankfully it seems that all they're really taking from the comics event is the basic premise, not really any of the details of what happens within the storyline). This might be the time where a character we've known for a while actually dies - something that really hasn't happened in the MCU yet (Quicksilver doesn't count, since he died in the movie where he was introduced - not counting his post-credits stinger in Winter Soldier). Nick Fury ALMOST died (but didn't), Bucky ALMOST died (but obviously didn't), Loki ALMOST died (but also didn't), etc. No major character has actually bit the dust yet. But it looks entirely possible that someone - possibly Rhodey - is done in by Civil War.
4. Bullets bouncin' off of Black Panther's vibranium suit HELL YEAH
Now if only someone can get Entertainment Weekly to retract that goddamn "Meow" cover.
5. Scarlet Witch vs. Vision!
Scarlet Witch and Vision have one of the more interesting relationships in the world of Marvel comics (they've been a couple for long stretches, despite him being an android and her being a weirdly-powered Magneto-daughter with a bizarre crown/tiara thing) - and Civil War finds them fighting on opposite sides, which means we're liking in-store for one of the first legitimate superpowered battles in the MCU.
6. The thing where Ant-Man flies around on one of Hawkeye's arrows!
We've covered the pairing of Hawkeye and Ant-Man before - and the comic/cartoon world's greatest pairing is finally coming to the live-action MCU, and we could not be more pumped. There's definitely nothing in the trailer as of this point (around the 1:53 mark) that has us more pumped, and we highly doubt there is any final moment in the trailer that would get us even in the same realm of pumpedness.
7. The "I could do this all day" callback
One of the best moments of the original Captain America film (known as "The First Avenger," a title that no one has ever actually used in real life) was tiny bobbleheaded Steve Rogers standing up to a bully in a movie theater and getting a thorough ass-whoopin' for it. The bully keeps punching Steve and knocking him to the ground, but like Chumbawumba, he gets up again ('cuz ya never gonna keep him down). It more or less perfectly encapsulates who Steve Rogers is - someone who won't back down from a bully and won't admit defeat against assholes, no matter how brutally stacked the odds are against him.
And now, again, Steve finds himself outgunned against someone who (from his perspective) is being a total asshole bully - Tony Stark. And while Cap has gone through a lot of changes over the course of the last 70 years, he's still got the spirit of that weirdly-CGI-faced Chris Evans in that alleyway back in the 1940s.
8. That Deadpool-lookin' guy ("Underoos"?) who shoots strings looks like a pretty neat addition
Hahahaha holy shit Spider-Man is actually really definitely in the MCU!
THIS IS REAL.
THIS IS ACTUALLY HAPPENING!