BtVS and Angel are great shows on their own, they don't need crossovers. Buffy and Angel are completely different people now. The crossover episodes were good at the beginning, in Season 1 of Angel and Season 4 af BtVS - The Freshman/City Of, The Harsh Light of Day/In the Dark, The Bachelor Party/Pangs/I Will Remember You, This Year's Girl/Who Are You/Five By Five/Sanctuary. (The Freshman/City Of - Not a large crossover, just the telephone call) 😀
The Forever crossover was good, beause Buffy needed comfort, and the There's No Place Like Plrtz Glrb crossover was necessary, somebody had to tell Angel. (And then the Blind Date and Disharmony crossovers were needed: for Cordelia to decrypt the files in Blind Date and the Disharmony one, which was very funny, was not only about Harmony, but also a way for Willow to tell Cordy, who probably told the others at some point, that she had experienced a few changes...)
You think I left one out? 😉 So, anyway they were great to begin with as Angel had only just left a few months ago. But as the characters have grown, there doesn't seem to be a need for crossovers anymore. But if they decide to do them, hopefully it'll just be one, and a darn good one too. 🙂