Tomie is one of my favorite manga, so ill try not to be as biased.
Now before you start reading Tomie, beware that its intended for adults only since it depicts extremely graphic scenes.
There isnt really a main Story, there are some minor and major arcs, there is one character, Tomie, that always reappears in each of the different stories though. Each story has something that makes it interesting in its own with different kinds of side-characters being impacted differently by the main character. It's hard trying to explain the story without spoiling so if this review wakes your interest you should definitely check it out.
The art-style is pretty unusual from what you normally see, personally I actually quite like the more depressing, realistic approach from Junji Ito. Considering the age of the manga it's quite impressing. It might be a bit off-putting for those who have only read the more usual stuff but you should definitely give the arstyle a chance.
As i said before there is one reoccuring character throughout the story and that is Tomie. So ill warn you now there might be some spoilers ahead!
Tomie isnt quite like other main character, throughout the story her actions and personality is similar, but the character is never actually the same person, she lives on forever basically. She also has the special ability to seduce any man she wants and make said man do a certain thing.
Again if you want to know more definitely read the manga.
I greatly enjoyed Tomie from the beginning to the end, it was different, it was special and it sometimes scared the living shit out of me. A great combination in my opinion 9/10