I did not review 12.10, because I escaped the release due to some reasons. However 13.04 seems a promising release. So lets get started.
Things that did not work
1. Even with Dell's effort via the Sputnik project, brightness still resets each time I boot the computer.
2. The dual graphics situation has not been solved. In this case AMD with Intel. Mesa does not handle the switching properly. As usual, I had to shutdown AMD cards using /etc/rc.local. In my case even the installation of propitiatory drivers from software updater failed and broked the Desktop.
3. Unity crashes, but the rate is far less than it used to be.
4. Application window randomly freezes (firefox, nautilus etc). These things often show up on computers with low graphics memory. Things had improved since 12.04. It is sad the problem returning again.
5. Even on installation that does not have additional repositories and is updated to latest revision, automatic bug reporter discards many bugs as not being default to Ubuntu.
6. Even though new nautilus looks good, it is one software that does not integrate with global menu. There is only Files menu on the menu bar, and that looks rather limited.
7. Though you can shutdown UbuntuOne synchronization using the cloud icon on top right, you can not shutdown this icon, or its listening mode.
Things that works or are better
1. Installation was fluid. No problem there.
2. Unity feels lot faster than its previous incarnations.
3. Runtime file search through nautilus is one thing that makes Ubuntu shine for day to day use.
4. Though I said menus in Nautilus looks disparate, things like sidebar icons, nautilus theme, and some new icons (Files, software center) makes Ubuntu a lot professional desktop.
5. New animations e.g minimize, snap etc has been improved.
6. New kernel version and mesa has brought improved graphics performance in some games. Users can enjoy many games with their integrated Intel graphics cards. Graphics performance still has some areas to improve, but everyday computing is vastly improved.
7. Ubuntu software center launch speed has improved, but things like multiple app installation and queuing needs improvement.
8. Show Desktop and workspace switcher has been added to Settings-> Appearance, and the switching between workspaces does not require multiple click anymore, and the transition is fluid.
9. You can use mouse scroll to switch between multiple windows of same application, and spread feature has been greatly improved.
10. Bluetooth is no longer dependent with wi-fi anymore, and that is a welcome change.
Linux by default, does not have problems relating to brightness, because one of the files under /sys/class/backlight works on all installations. However, since the brightness feature does not work out of the box in Ubuntu, and user has to manually set it, it should be considered a bug.
Many games are coming to Linux, and some of these games require propitiatory graphics drivers, Ubuntu should make installation or removal of these drivers painless. Installing or uninstalling these drivers should not leave the system in an unusable state. I have been playing with these settings since the beginning of SNA drivers, that's why I know how to bring back the Desktop from these failures, but for most users this is unacceptable. Things like brightness, graphics performance and power saving (it is good to see SNA enabled by default), easier installation and removal of software needs more attention. There are still some days left for the final release. I hope some of these issues gets fixed.