I watched the Winter Soldier the first day of its release. It is an entertaining and engrossing action thriller. Considering Captain America is not the one among the Avengers with what we would consider "super powers", the plot, action and acting in the movie makes it leap to the top pile of best Marvel movies. In terms of pure fun, I would rate in just below Avengers (watching all heroes in one screen is AWESOME). The hand to hand combat scenes are amazing. The comedic and yet witty one liners are great. Even Sam Wilson a.k.a The Falcon does not seem cheesy for the screen. Scarlett Johansson and Chris Evans have a wonderful chemistry and dialogues between each other.The movie depicts the Cap struggling with life in modern world and understanding it. His diary writing of things he needs to catch up on is a fine touch. Personally, I think Bill Gates should also have been there! :) The movie also touches on other modern issues like spying, public freedom and does a good job at it in my opinion while still being simple to understand.
The villain, Winter Soldier, is well portrayed by Sebastian Stan. I read about the Winter Soldier comics after hearing news that a movie about him is going to be made a few years back and it is an interesting storyline. It was a cool shot in the movie when he just grabs Cap's shield swung towards him at full speed.
Overall, an entertaining movie.
P.S. The end credits scene with the twins is amazing. Somehow, I got the glimpse of next Avengers being much darker watching that scene.