What I really like is when the lady makes it clear that she's happy to be spending time with me (whether for real or she's a good actress), and acts affectionate. The same sort of little gestures that mean so much when dating make a difference in these encounters, too, like reaching out and holding my hand, touching my face, hugging me, and, most of all, smiling.
Enthusiasm - seeming to be glad she's where she is, doing what she's doing, enjoying giving pleasure, and receiving pleasure make such a difference. (Fake smiles, "aren't you done yet," turning her face aside when attempting to kiss, and such are a real let-down and turn-off.)
And as has been already mentioned, one of the biggest disappointments is not being able to finish on my schedule. Don't want CIM, fine, say so before starting. But if you say you're okay with CIM, don't stop what you're doing until he stops. There is little that's more annoying than being evicted form a nice, wet, warm mouth right when my entire being wants nothing beyond remaining right where I am. In my opinion, one of the nicest things a woman can do for a man is to keep him in her mouth, gently, until after complete "shrinkage." (I wouldn't expect this if you're not a swallower, but take at least some time, please, for me to just feel good and enjoy.)
And while the stereotype is that gals want to cuddle but guys don't, well, for some that may be true but don't act as if it is. While not as annoying as mouth eviction, having a lady jump up immediately after I've come so she can get a wet towel spoils the moment, and thereby the experience. Yes, a hot towel is great -- but at the proper time, which is after my heart has slowed and I've relaxed. Be cuddly, and if it's not reciprocated, fine - jump up for the towel. But if he cuddles back, that's where he wants you to be.