Goody, un-intended debate!
Technically, you have contradiction. Even though the Sega CD was an add-on to the Genisis console, it didn't require the cartridge port, and it had it's own CD games. The most it required from the Genisis was its hardware to run it, and a stand alone Sega CD was being planned at one point anyway. By this definition, it is the same as the Saturn, and therefore if you argue that the catridge isn't required for the games, then CD gets included.
So, that means that either the Sega CD is the first dedicated disk reading system by Sega, or you have to say the catridge port nulls it all together, which at the same time takes out the Saturn, leaving us with a disk reading ONLY Dreamcast console. Boy do I love friendly debate ^^
Getting back on topic however: Even though everyone says that the 3-D Sonic games all blow, I loved the first Sonic Adventure game, and the second, on the Dreamcast. My favorite memory was playing as Sonic in the (either second or third) stage, where you get sucked up by a tornado and all of the sudden you're super high up. And for whatever reason, I didn't follow the grating path that led down, I turned Sonic to the opposite side of the floating island, and leapt right off. Half a minute later, I landed on the final island at the bottem with a time that was nearly half of what I usually clock in at on the stage.