Sadly, Angel's character was totally wasted in X3. He had barely any interaction with other characters beside his father. If the movie was longer, there would've been time for another danger room scene where he was training with the others after he arrived in the X-mansion. Then he could've been a true part of the battle line in the final battle. It would fit with him coming to terms with his decisions and who he wants to be. And it would've been cool to see him rush into the enemies from the sky or evade burning cars Magneto throws at him.
I wouldn't have mind if he came back in DOFP.