I'm sure the download size is because they have to include SDK binaries for each vendor whose format they support.
Pretty disappointing performance to me. They brag about using caching for optimal performance, but either they don't do read-ahead caching, or there's a bug. Once the current image is rendered it should start rendering the next one in the background. But it apparently doesn't, because no matter how long you wait, when you hit next you still get stuck viewing the low-res preview for at least half a second before getting a high quality preview. Slideshow mode doesn't force the low-res preview on you, but it still doesn't seem to use read-ahead caching so the performance is pretty slow. The slideshow feature in the CS2 Bridge is much faster (just wish I could change the BG color for it).
This viewer has limited capabilities if you're using ThumbsPlus or some other type of viewing program. For people who you want to share your NEFs with (give them their negatives in essence) it now enables non photo geeks to view RAW camera files.
However, I think I've found some serious glitches in this program.
1. When deleting single or multiple image files (NEFs, TIFFs, etc.) Windows XP throws a cannot delete file error.
2. After uninstalling the Windows RAW viewer, I no longer get this error.
3. After uninstalling, I no longer have NEF thumbnails in Windows Explorer.
4. In order to restore thumbnails in Windows XP, I ran the latest Capture update and it restored the thumbnails for NEFs.