I also transferred my music and iTunes library from one computer to a new one.
I searched high and low for information about ratings and play counts and while there was a manual trick for ratings, I couldn't find any means of updating all play counts in one go, so I ended up writing a program to do it - which I am happy to share if you email me (I'd attach the files to the forum but it doesn't appear to be possible to add attachments to a post).
First ratings - manual, but easy. Go to your old iTunes machine, create 5 playlists - called e.g. rating1, rating2, rating3, rating4, rating5. Then sort your music by rating, select all 5* and right click add to playlist and choose rating5. Similarly to the other 4 rating levels. Then go to File->Library->Export Playlist... and export the 5 ratings playlists with suitable names - they end up as text files. Move the 5 text files to the new machine and File->Library->Import Playlist... Once the playlists are loaded, go into each one in turn, select all tracks and right click to set the rating level. All manual but pretty quick and easy to do.
Play counts are not so straightforward. The play counts are stored in an xml file in the same directory as your iTunes library. I have written a java program to read both old and new xml files and then to pull the play counts from the old xml file to the new one. However, iTunes doesn't read the xml file after you've made the changes, you have to force it to by renaming/deleting the iTunes library (binary) file (not the file with songs in, just data); then when you open iTunes it appears empty - but don't worry - go to File->Library->Import Playlist... again and this time import the xml file output by my program. After a few minutes of processing everything is back including the updated play counts. This link is to a post that talks about this process of rebuilding the iTunes library from the xml file:
http://www.makeuseof.com/tag/how-to-fix-repair-the-lost-link-to-the-itunes-music -library/
There are two issues that I found with following this process, both to do with synching devices to iTunes. I have an iPhone and after synching the applications did not show up in iTunes. So to fix this I plugged in the phone waited for iTunes to detect it, then right clicked on the iPhone device in the left bar of iTunes and selected Transfer Purchases - this pulled the applications across from the iPhone to iTunes and then I was able to sync the iPhone completely.
Second issue was with my AppleTV, which simply didn't appear in iTunes despite on the AppleTV still showing connected to my Computer. My fix for this was to disconnect and then re-choose the computer on the AppleTV, enter the pass code in iTunes and re-connect it again. When AppleTV re-appears in iTunes, you have to input all the sync settings and let it sync again - which is a pain, but having put in the sync settings it just gets on with it - so it wasn't a problem apart from the time it took to re-sync.
If after that explanation you would like to try my program send me an email and I'll happily send you the zip file containing it. You can contact me: tim AT hedger-gourlay.com
