Though he finished his first objective, he failed to get Cap's shield and Vibranium, which displeases his master.
While the other synthezoid Avengers took care of their counterparts, Vision was sent to capture Wasp. He exhibited human emotions as he talked like a human instead of a machine after taking her out. He questioned his master about this, but Ultron refused to answer.
After discovering Cap's infiltration into his base, Ultron ordered Vision to finish him off. While fighting, Vision asks why Cap keeps fighting, to which the man replied that humans are fighting for others instead of themselves, and never give up. Hearing Cap's words, Vision deliberately released the Avengers out of their stasis containment tubes.
As the Avengers battled Ultron, he helped them by phasing through its neck and disengaging the locks connecting its head to the body. This allowed Thor to smash the head off, causing an overload in Ultron's power core which burned the base to the ground. After Cap saved Vision, he asked why he helped them defeat Ultron, to which Vision replied that he views humanity as more consistent with his ultimate goal of perfection.
Somehow, he was fully repaired and seen attending the funeral of presumably-deceased Hank Pym and talking to the other heroes he meet after hearing Stark's speech.