Its all about the characters. Spike, Jet, Faye, Ed, Ein, Vicious and the lovely and eneigmatic Julia. Cowboy Bebop has some of the deepest, most human, most memorable and facinating characters you are likely to find anywhere, heck even the background characters who only show up for a single eipsode are fairly well fleshed out. I'll admit that the eipsodes can seem slow and meandaring... if you are looking for a plot. There is no plot, even the show's "metaplot" isn't really a plot. Bebop is sci-fi western noir; all there is is characters and situations and characters interacting with each other and working their way through situations. And if the show has done its job right then the last three eipsodes should hit you like a sucker punch in the gut. In some ways I think that the entire show is just a set-up for the finale.
Also the show is filled with some very subtle details that you don't, that you can't, notice the first time through. Foreshadowing of major events, commentaries and analysis of the major character's personalities carried out in some inventive ways, repetition of themes that don't make any sense until you can pull back and view the work as a whole. There is a lot of craftsmanship that went into the creation of that particular show and sometimes it is possible to appreicate it just for that fact (remember too it was made in '98, the production values were ground-breaking for the time).
And there is of course the music. Tank (the opening theme) and Real Folk Blues (the closing song) are very good of course but I am very partial to Road to the West and Words That We Couldn't Say. And of course there is Blue, I swear that song makes me tear up every time.
So yeah, thats why I like the show. YMMV.