The long series are still good entertainment as always, but I think series that have very limited episodes are a lot better because all the art and storyline focus is maintained into each episode, unlike in a longer series where there are a lot of episode recaps, repeat animations, and single scenes that span a few minutes in real life but last four or so episodes in them (The third Hokage versus Orochimaru, anyone?!)
Short ones I really like are Sentou Yousei Yukikaze and MsigLoo. The only problem with the short ones are that the other untold details are often left for the viewer to research either through the web, in a magazine or via rumors. Sometimes, though, it could mean joy for other people (Tomino followers, for instance.

)