Classic Fountain Pens

Fountain pens are more or less the same shape and style.  The real challenge, then, is to make the pen's design interesting without compromising the basic principles of what makes a pen functional.  A pen would not work if it were an inch thick and a quarter inch long.  The user would be unable to support their writing motion with the rest of their hand and would tire quickly.  Nor would a pen work if it were thin as a nail and several feet long.  Once again, the user's fingers would quickly tire from having to work to hold such a thin, ungainly writing implement.
However, the color and texture of a fountain pen are limited only by the designer's imagination, and small variations in the traditional blocky cylindrical shape can be made, as well.

This is a typical fountain pen design.  It is a fairly standard design: it works because its design compliments its function, and it retains subdued values that invoke a sense of classiness and nobility.  People who bother with the hassle and mess of fountain pens typically enjoy either the old or the expensive, or both.  This pen fulfills both of these design "needs" well.

This is a slightly louder design.  The colors are all bright, simple shapes on a plain white background.  This pen is less classy, which makes it less attractive in my opinion.  The designer was obviously trying to make a piece that says "I'm classy enough to use fountain pens, but I'm not a wet blanket.  I like to have fun," but I think the overall effect comes across as merely gaudy.

This pen is ridiculous.  It is encrusted with hundreds of tiny diamonds, and the manufacturer's logo is etched with tiny rubies.  This design reminds me of "bling" - It is wealth without class.  Strutting this pen around (or displaying it on your office desk) is merely making a statement: "I have more money than you."  If that is the intended statement, then this design works well. 
Otherwise, maybe place only one large diamond on the pocket clip instead of hundreds of smaller ones plastered all over the outside of the pen.  Make it more tasteful, and it would be a much better design.