They shouldn't have killed off either Luke or Darla so soon. Angel would have (obviously) recognized Darla, and, because she is family, so to speak, he would have spent several episodes trying to keep Buffy from meeting her and trying to get her to leave town. That would have been when Angel being a vampire would have been revealed to the audience, but Buffy wouldn't find out right away. Angel's motives for being in Sunnydale, as well as his past history, would remain ambiguous for awhile before his past would be revealed, possibly when Buffy has her first fight with Luke, and Angel helps her, with Darla (who "kills" Buffy temporarily before Xander revives her) being staked in the process, revealing his vampire status as well as that his being there was honorable.
At least one episode would be devoted to Buffy reconciling her feelings for Angel and accepting that, a vampire he might be, but evil, he apparently wasn't. (The key word there being "apparently")
The Season finale is a fight with Luke and several other of the Master's minions. Angel is fighting the last two while Buffy faces the Master alone. Out of sight of Buffy, Angel stakes one vampire, but is about to be staked, himself, when a black clad figure steps out of the shadows and literally tears the last vampire's dead off. The dust clears, and Angel is staring at his savior. "Hello, Peaches, We too late for all the fun n' games?" Spike.
(The Season ends with that scene)