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.
Many fans are elated at the inclusion of Natasha as a major character. Others, however, are upset that her involvement seems to be effectively subsuming the role of Agent 13.
Cap's new uniform for the film has also gotten a mixed reaction, with some declaring it to be an upgrade over his costume in The Avengers, and others lamenting the removal of the red-and-white stripes from said costume.
It Was His Sled: The Reveal of the Winter Soldier's identity was an 8 year old spoiler for comics readers by the time the Winter Soldier film came out. The anticipation of the film is actually a result of this, wherein the drama surrounding this is the main reason why fans want to see the film.
Some Italian fans compared Winter Soldier to Adam Kadmon. He's also been compared to Raiden, thanks to his mask, Super Reflexes, and cybernetic limbs.
"The Helicarrier's becoming the Enterprise," in a reference to how the thing keeps seeming to die whenever we see it.
Ship-to-Ship Combat: Some rather rabid shippers are already voicing opposition that Bucky may become a potential love interest for Natasha (Black Widow), thus sink their hopes for a Clint (Hawkeye) and Natasha relationship. Though this assumption isn't without some merit, due to Bucky and Natasha having actually been an Official Couple in the comics.
And now, with the emergence of on-set photographs showing Steve and Natasha kissing, both are threatened by the emerging ship.