Captain America 2 takes Captain America, removes his clear enemies (Nazis, Hydra, Chitauri), and emphasizes how he's all alone, out of his own time. (The Avengers did the out-of-time shtick more superficially and amusingly, emphasizing that Steve Rogers doesn't know popular movies or that he's the subject of collectible cards.) This ramps up the uncertainty... or at least it should.
But when a film casts Robert Redford as a previously unknown but powerful character, and when we suspect that someone is really a traitor, it's like when Law & Order has a famous person: we know who the bad guy is. Similarly, when Captain America is alone romantically and ends up kissing Scarlett Johansson, I don't really wonder if maybe they'll become an item; or when Captain America attempts to reform his friend-turned-brainwashed killer, there's not much anxiety about whether it'll work.
So while Captain America 2 poses itself as something of a paranoiac political thriller, dealing with contemporary issues of the security state and over-surveillance and big data, it doesn't really land any of those punches. Critics and friends lauded that commentary on contemporary issues, but it felt pretty flat to me: "How much is security worth?" is an interesting question. "Can we morally kill an innocent if our big data analysis says this person will be a problem?" is a less interesting question. "Can we sacrifice freedom if it insures security--and, oh yeah, Hydra will be in charge?" isn't even a question at all--it's a call to arms.
Part of the failure of this film for me is encapsulated in the hostile takeover of SHIELD headquarters during the launch of the three new super-helicarriers: if your super-secret society is a few minutes away from taking over control through manipulation and subterfuge, why bring out the guys with the guns? Instead of ramping up tension, all that does is replace uncertainty with certainty. Which turns paranoia into a boxing match and clears up any problems that Captain had. After all, more than friends, Captain America needs a clear enemy.