I love the Dreamcast controller.
I honestly find myself wishing that more controllers had cords that came out of the bottom of the controller, especially since my PC case is on the floor, and it just makes sense for me that the cord would already be going downward toward the floor.
As far as the "hollow" feel of the controller goes, I don't think it's so much an issue of the controller feeling hollow as it is that the controller just feels a bit too light to me. That could be because I'm not used to playing with a VMU and a Jump Pack in the controller, though.
The d-pad is fine for me, but I will say that the Dreamcast controller's d-pad does tend to have a higher failure rate than that of d-pads on other official Sega controllers.
I'm a bit torn on the issue with there only being a single analog stick. The Dreamcast controller is one of my all-time favorite controllers, but the 3-button Genesis controller is my all-time favorite. A lot of people feel that the 3-button Genesis controller had too few buttons, but I don't think that's true when you consider that the overwhelming majority of Genesis games didn't need or make use of six face buttons. The problem with the Dreamcast controller is that even Sega itself released plenty of games that really would've benefited from a second analog stick, which makes the choice to have only one stick flat-out bizarre. There are certain games that some people would consider to be "better" with a second analog stick, but I'll disagree in some cases. MDK 2, for example, is best played on a Dreamcast controller, in my opinion. Moving with the face buttons just feels right.