I don't think it's quite fair to dismiss Cullen's fans as shallow.
The morality of Templars versus mages is complex, and Cullen has gone on a long journey over three games. From nervous and naive recruit, to traumatized reactionary, to a Knight-Captain who struggles to remain just after he's been burned, to the man who finally stood up to Meredith and said no, to the General of the Inquisition who devotes his whole being to a righteous cause, all while battling lyrium addiction.
I was merely okay with Cullen for most of DA. It only took a few scenes in Inquisition for me to see what his fan club had been talking about all these years.
I started out as a faithful Cullenite. I had every intention of making him my first play-through romance. Per the plan, I began flirting with him at every opportunity, fawning over every little adorable detail, remembering the days I had my Circle Mage from Origins feebly attempt a flirt (ooh, forbidden romance, the best kind!)
Then I got
by fade-tongue, and the rest is history.

In all seriousness, the series of unfortunate events that Cullen endured, make him a very interesting character to me. A templar, having sworn an oath to the Maker, to the people, to himself, to aid and protect his charges, never to abuse his position, and try to make the world a safer place. His sheer will and faith have propelled him forward in a, generally, morally-sound direction. He doesn't take himself too seriously either (regardless of what Varric says, haha!) His nerves with women are right near the surface, which make him endearing and not unattainable. I rather enjoy seeing a grown, mature man, one who is relatively sure of himself, sound and resolute in his convictions, with high morals and a humble spirit; become a gooey and giggly mess over the charms of a woman. *breaths in deeply* Ahhhh, the secret power we hold, ladies. (and dudes too, and... little puppies, and kitties, and... I'm getting off-track)
Now, if only Solas would kindly cease and desist, and become the putty in our hands we so desperately crave.
Phew! Uh oh, I feel a bit warm after that. I-I think I've got a fever... and the only prescription is more...(wait for it) ...fade-tongue! 