I heard he wasn't happy in ECW, but i later heard he liked the idea but knew that he was off to Smackdown soon.
Vince fired him because Angle wouldn't go to rehab, as WWE Officials thought he was addicted to painkillers. Angle refused, meaning Vince had no alternative but to fire him. (Vince Suspended him before, didnt work).
I'm not a big fan of Vince but it does seem like he was looking out for Angles health, the MMA also were checking out his health. Hopefully TNA do the same. As I've said it before Angle will die or be serioulsy hurt if he keeps pushing himself the way he is, and joining TNA where they have less restrictions on wrestling moves, is it the best idea?