Yep, the factory nav is very good. I've got a Becker 4765 head unit in my ES. The options are very good, it has some nice features and the voice prompts are excellent but as you say the display is only the dot matrix readout on the head unit. It doesn't matter too much as the voice prompts make up for that. If you are talking about the nav unit on the Metropolis, I think the colour display screen is pretty small but it does display a map. The fact that it is factory means it is all tied up to the head unit and you can still listen to CDs and radio whilst getting the prompts.
The only real concerns I have with my factory nav is the lack of screen and the lack of speed camera warnings. I would still recommend it though.