i think a lot of it has to do with what is in your head; after all, your brain is still the sexiest organ you got. i will also support what
@Alex22876 said that technique is also very important. i've received a lot of head from various women in my life and some were just god awful bad... such as too much teeth, no enthusiasm, not enough saliva, too much grip, not enough grip, and the list goes on and on.
back to what i said about it being in your head... getting a blowjob to me is like watching a show. you want the show to be entertaining and fun and pleasurable all the while, at the same time, you want to see that she is enjoying it too. so this begs to say that it has to be the combination of all the above unless you're just a horndog and just glad someone is sucking your dick.
for me, my wife has figured me out, so i like her to tease me with lotsa of sloppy sounds and moaning from her to tell me that she's enjoying what she's doing to me. i like it when she tells me how much she loves sucking my cock and also how she's not afraid to look me in the eyes while gobbling down my meat. i appreciate her using her hands while she sucks me (kinda like a hand-job-sucking action). i also like it when she comes up for air to kiss me while continuing to stroke me then go back down. lastly, if she plays all the above well, all she has to do is verbally beg for my cum and i'm gone.
my advice: take some time to reflect and see what "truly" turns you on about being sucked and go from there. once you figure it out, don't be afraid to communicate that to your partner and hopefully your partner is more than willing to give you what you want.