When I first switched to Mac, a proper Mp3Tag alternative was the first thing I really missed. It took me quite a while to find app with similar functions and ease of use and I probably went through 5 different apps before I found Metadatics. For a while I was actually using Mp3Tag through Parallels.
Metadatics is very similar to Mp3Tag and once you get used of it, you will not miss Mp3Tag at all. Interface is very intuitive and you get hang of it withing minutes. App itself is fast, and developer updates it (as of this writing) frequvently. Album art and meta tags searches are all done through MusicBrainz which works pretty good.
You can find more about Metadatics at: markvapps.com/metadatics/ and you can buy app through App Store or directly from the website. Free demo download is available too. Price in the App Store: $9.99 which is very reasonable for this app.