Sounds great but MAJOR installation issues
I was having major issues after more than a week of repeated downloads and installs, wherein I could not get the software to appear in Logic 9. For the record, I tried every user forum and the mfr.'s tech support, to no avail! I am a successful user of Superior 2, SSD 3.5, and Addicitive Drums, as well as several other plug-ins and virtual instruments, so I have no idea why I had such an issue with this install. Judging from all the posts on the various forums and websites, etc. I can conclude that I was most definitely NOT the only one having issues. Steven Slate himself also acknowledged in an e-mail to all SSD4 purchasers that there were installation issues.
The good news, however, is that it did appear (quite spontaneously) on its own one day, a few hours after I decided to give up! I literally walked away from the computer for several hours, and when I came back it was listed in the AU manager!
And I must say that the drums sound great! User interface is better than SSD 3.5 (no more Kontakt Player - great news), and the program works flawlessly now.
In summary, it sounds great, but was so aggravating to install that I can't necessarily recommend it over the other programs. Therefore, I have deducted one star.