Improve file naming: it skips spaces, leaving filename as one long character chain. It also leaves some additional number on the end of file name.
When the track is from no album, it copies filename to the album tag. It is a con in my opinion.
Poor sound quality.
I think you could improve by giving people a setting page with some settings like bitrate, type of naming and tag filling, download path.
Improve the above and the extension will be strong 5 star.
Really good downloader so far.