There are plenty of reviews of Aperture around the web already, but I’ve commented on Aperture, Lightroom Beta, and six-color channel mixing in the past, so I’ll just add my two cents: Aperture 1.5 is really, really easy to jump right in and use. It has 6-color adjustments, one of the cool Lightroom Beta features that had me mesmerized for a while, though it looks like the monochrome mixer is still 3-color.
I think it was a great move on Apple’s part to offer a free 30-day trial, because I’m much more likely to purchase it after having the chance to try it out.