The wish is a very well written episode and its a dark look into what could have been without Buffy.
Cordelia comes back to school after her injury and finds that things are very different for her. She no longer is miss popular and her old friends laugh and make fun of her. Feeling down she realizes that all her problems started because of Buffy and sheinadvertently makes a wish to the new girl Anya, who just happens to be a vengeance demon.
Cordelia wishes Buffy never came to Sunnydale and soon finds herself in an alternate reality where vampires reign supreme, the master is still alive, and where Xander and Willow are super scary vamps.
Now at this point they could have made this episode a typical alternate reality episode where the person throughout the episode learns just how bizarre their alternate reality is and then tries to change it. And in the beginning Cordelia does just that. But things take a turn for the worse when Xander and Willow kill her.
I think that that was an interesting twist to a story idea that has been rehashed many times. The whole episode is well done. Xander and Willow are terrifying as vampires and its a good setup for Dopplegangland where vampire Willow makes a return.
The alternate Buffy is also very interesting. She almost reminds me of Faith and I wonder if that's what the writers were going for. She's tough, scarred, and dark with none of the fun loving Buffy we all well...love.
The end scene in the warehouse is well done. We watch as all of our favorite characters die. The part where Angel gets shot and says, "Buffy." as he turns into dust is sad, but also made even sadder because Buffy doesn't even care. She walks right through him as though he didn't matter.
Well written episode, great to watch, and its interesting to see how much Buffy has done for Sunnydale.