Every single thing.
The anticipation when my lips are slowly kissing and licking their way down her stomach towards her pussy. When you start kissing and licking her inner thighs, how you can feel how warm her pussy is right before you lick it. How she moans the first time you actually lick her clit. How she grabs my head and looks down to see me with her clit in my mouth. How you can feel and taste how deliciously wet she is. How I can feel her pussy contract while I finger her and my tongue keeps licking her swollen clit. How her breaths get deeper the closer she is to cumming. Hearing her tell me she is getting close to cumming. Hearing, feeling, and seeing her cum from my tongue. Holding her down while she squirms while she cums. Feeling her squirt is an added bonus.