For me, it's several things:
1. First and foremost, the enema must be REAL. I prefer bag enemas.
2. It needs to be from a FULL BAG. Some of the e-videos really cheat. She needs to take it all. No cheating.
3. It needs to be the WHOLE BAG. Giving a few drops of water just isn't realistic, nor is it what I would require if I were the giver.
4. It needs to show the insertion.
5. It needs to clearly show the bag emptying into the receiver / clear tubing is a plus, with soapy water, so one can see the flow. Clear water's not bad, but soapy is better.
6. It needs to involve realistic reactions. Fake screaming, whining, etc. are just stupid. I've given hundreds of enemas to women, and I never got the reactions I sometimes see in videos, because they are fake. I didn't give tiny enemas, either. 2 quarts plus. Always.
7. It needs to show the bag AS THE ENEMA GOES IN. Why? Then you know she got the enema.
8. It's good to have a toilet scene, so you can gauge whether or not she got a real enema. Reality based, Visible Expulsions are appreciated, but not necessary. What IS necessary is to know she got filled.
9. Inflatables and large nozzles being inserted are enjoyable to watch, but cruelty is not, unless only a pencil sketch. I've seen some videos where it's obvious that the purpose is to hurt or harm. I assume they are consensual or at least consensual/nonconsensual, but I actually am concerned for people who are mistreated. Some of these are erotic classics, but...
10. If it is a scenario that emphasizes sexual contact, that can easily spoil the video, because the enema ceases to be the focus and the sex becomes the focus. A true enema lover wants to see THE ENEMA.
11. I like enemas where the enema makes sense, either from a medical or erotic or BDSM perspective, not something that's dumb or impossible to have happen.
As I said, I've given many enemas. I love to give and I love a compliant partner, meaning that I love someone who knows she's getting an enema if she sees me--or at least is willing to accept whatever happens, without complaining too much. Some whimpering and groaning is good, if she cramps. I prefer her to enjoy the process and be accepting of it. Many of my play scenarios involve an enema that was unannounced until the bag came out. If the woman is into medical fetish, it's unlikely that she will resist, when told that it's necessary to be clean for the rectal exam. In such scenarios, I generally give 2-3 enemas from a 2 quart bag, filled completely.
If I'm receiving the enema, then I enjoy a giver who understands the importance of the stimulation involved, is committed to giving the full bag, is caring (I can't quite take a full Klystra bag since my surgeries), and is helpful when it comes to afterplay (prostate massage, etc.). When receiving, I prefer "enemas till clear," which generally takes a fair amount of time, and when I have seen Pro-Dommes, I let them know that I expect to get completely cleaned out.
That's all I can think of at the moment.
Comments welcome, especially from women, but anyone is fine.