Response based on 2010 Landcruiser with a Middle East maps covering Saudi Arabia, Bahrain, UAE, Kuwait, Qatar and Oman.
1. Overall, do you like it?
In general, the complete user interface of the Toyota system, and that includes all functions of the touch screen unit like audio, navigation, telephone, is slow and cumbersome (actually pretty awful is a better description) to use. Specially when compared to good and intuitive user interfaces of e.g. Ipod music player, Garmin and TomTom navigators, etc. The biggest let down however is the disabling of basically all functions when driving making the system completely useless.
2. What features do you use the most? The least?
Due to the very limited map coverage the system is only useful in the center of the major cities. Due to the difficulty of transcribing arabic street names into English it is rare to be able to find the correct street by entering the name. The only thing that is really useful is the ability to either enter directly on the map or use lat/long. Both however imply that you know where you are going...
The least liked feature is the voice guidance, I always have this turned off. Its a distraction and often confusing in all but the most straight forward situations.
3. Hows the interactivity? (How easy can you select stuff)
See my answer on 1 and 2 above. As soon as you are driving no interaction possible, maybe safe but utterly useless. While standing still its reasonable but pales in comparison to Garmin and Tomtom
4. Do you get lost often?
No. but this is not due to the system

The indicated route is often longer or less optimal than it can be. Not sure this is the system, most likely caused by the limited map detail.
5. top 3 best features, top 3 worst features?
Best
1. Fact that it is build in, no separate devices, cables, wires, rattling around
2. Reasonable screen
3. ?
Least
1. Slowness and disabling of functions when driving
2. Poor user interface
3. Limited map detail, specially when compared with separately available systems
As you may have guessed from the above, I do drive around with a separate Garmin unit loaded with detailed Saudi maps including so called Darmoja desert maps and a table PC loaded with Oziexplorer and cached GoogleEarth images.
While this doesn't help finding addresses, in particular for off-road driving this combination is vastly superior to the Toyota system.
Good luck,
Nan