What makes a great manga/comic.

I am very interested in creating a web comic, but I lake the knowledge of a great cohesive story line. I have only read a few mangas that I consider good. In particular Great Teacher Onizuka, I love how he could incorporate slice of life, school life, and action all into one manga. Does anyone have an manga/comic that they consider very good, and by good I mean that it has a solid story, and very interesting? I am open to need ideas.

Some series that I enjoyed was Elfen Lied, Trigun, Samurai Shamploo, Love Hina, Chrono Crusade, Mezzo, Monster, Gurren Lagann, Samurai X. That is a brief anime bio so that you know my tastes.