I've commented here on several threads about all the pleasant and favorite things about taking an enema, including much as OP just described, all the way from preparation to insertion, filling, etc. through to holding, orgasm and expulsion. It's all a great sensory and sexual experience. Especially with a trusted Domme partner forcing and guiding me through it all. I especially love large volumes held for long retentions. But just now, I think my favorite part just occurred to me.
Perhaps a bit harder to describe and variable in execution and duration, but possibly the best erotic thrill or satisfaction is actually having that trusted Domme partner, who I've been lucky enough to have IRL a few times in an ex-wife and exGFs. She was very good at giving me forced enemas in our consensual D/s sex times together, and mixing all my other kinks in with the enemas. We were both switches and she sometimes loved to switch roles and become my sub to let me give her enemas. All the usual sensory delights of an enema are wonderful, like insertion, inflation, filling, massaging, holding, and of course orgasm, etc., but perhaps the best part during any or all of those enema phases is feeling her have complete control over what I had to do for her to be submissive to her whims long and hard enough to earn an orgasm and then expulsion. It's a mixed thrill plus dread whenever she would tell me things like she'd do whatever she wanted to me, make me start the enema, or increase the flow, or feel a rush as she pumped the Higginson bulb into me, or make me hold it for so long, or just smile or laugh at me when she knew I was struggling to withstand something from her. The physical acts themselves were delightful of course but knowing I had to do as she demanded and watch her enjoy her dominance while knowing we were equals again after my ordeal, is really icing on the cake (and very thick delicious icing at that). Perhaps it meant that I drew immense satisfaction akin to love in her willingness to subject me to any and all my kinks intensely enough to give me satisfaction and finally orgasm, no matter how long or intensely it was. And when we switched occasionally, of course I would give her the long intense submissive enema/kink satisfaction she craved and loved as well.
All of this is accurate and true, but it feels like I haven't conveyed the real essence of it as well as possible. If I can find a better way to write or explain this, I'll try again later.
Eric