The drive makes use of MLC flash, which is undoubtedly in the interest of cost. This compares to the company's Vertex SSD series, which includes drives that use the more expensive (but more reliable) SLC flash. OCZ pitches it as a solution for desktops and workstations that require a performance boost.
For the most part, SSDs have only come in 2.5" or 1.8" varieties. That has made a lot of sense for a while, as the biggest early market for SSDs is laptops, where those sizes are standard. As more people want to use SSDs for desktop use as well, it makes sense for manufacturers to take advantage of the more common 3.5” bays inside desktop chassis.
Whether or not that the 3.5" size has contributed to the Colossus capacity and performance specs isn't mentioned. One other interesting note is OCZ's mention of wear-leveling. OCZ made it a point to indicate the actual available space on the drive will be less than what is on the label, due to upwards of 5% of the drive capacity being reserved for wear-leveling purposes.
If these drives sound awesome, it's because they are -- and OCZ knows it. While the 3.5" form factor might make it easier on desktop users, the price probably won't. The 1TB Colossus was supposed to ship last month for $2,500, and 250GB drive is listed on Amazon for $1,122.99.