The MCU has a lot to offer in all phases. The first phase while good does have a couple weaker films. The best from Phase 1 are Iron Man, Captain America: The First Avenger, and The Avengers. Iron Man 2 is the worst not only of Phase 1, but the entire MCU. The fact that Whiplash takes a backseat to some jerk in a suit really sucks. The climax is really disappointing with how quickly Whiplash is defeated, and Tony is a complete moron in a number of scenes. That party scene is horrible. It's also bad how Jon Favreau's story was really interfered with to make the movie a commercial for The Avengers. Thor was cool, but not the best. Still good though.
Phase 2 for the most picks things up. I quite liked Iron Man 3, but felt it had the same villain problem as the second film. Captain America: The Winter Soldier, Guardians of the Galaxy, and Ant-Man are the best in this phase. Thor: The Dark World is okay, but kind of forgettable. Weakest of the Thor movies. Avengers: Age of Ultron while enjoyable is the weakest of the Avengers films. The film still had some good ideas, and Ultron was quite compelling as a character.
Phase 3 is pretty consistent throughout. Many of the best films are in this phase. Captain America: Civil War, Doctor Strange, Guardians of the Galaxy 2 Spider-Man: Homecoming, Thor Ragnorok, Black Panther, Avengers: Infinity War, Ant-Man and the Wasp, and Avengers: Endgame are all either really good, or flat out amazing. I still haven't seen Spider-Man: Far From Home, and Captain Marvel while not bad is the weakest of Phase 3.