I loved Julian when he first moved into my town, but since then I slowly grew to dislike him as I found him creepy (his white eyes specifically). When he pinged me to stop I actually let him go (I wish I would have at least given him away to someone who would appreciate him but I completely messed up with that...).
I tend to love a lot of the tier 1 villagers (Merengue, Lolly, Ankha, Zucker, Fang to name a few) but Julian I just don't like anymore. It does seem like out of the most popular villagers though that Julian has the most divisive reaction by players.
I guess it's because he's unicorn or something like that. I don't get him either though Buut I love Marshal and I understand that he's popular, cause he's adorable male squirrel after all.
I think he's popular because of his design since he's a unicorn. I guess his house decoration helps too, I'm not a Julian fan but I like the way his house is decorated. I don't see the appeal myself otherwise (and I totally don't get why people love Marshal so much above the other squirrels) but I guess everyone just has a different taste.
I personally don't like Julian. When I first met him in my town, I thought he was a girl because he's so feminine it's unreal. There are so many better villagers in my opinion, such as Caroline, Drago, Phoebe etc.
Julian is overrated just because he's a unicorn, and I've never really liked his voice anyway.