Very good already, not yet 5 star material as the customization options are not deep enough and/or are as of yet unelegant/convoluted. Some very obvious stuff is not implemented at all.
Just a taste:
-There are several greetings according to the time of day (Good evening/night/morning/etc), yet neither the times at which they are displayed nor the messages themselves are customizable beyond adding your name.
-You can't assign pictures/collections to different times of day. (Sunrise pics for 'Good morning', etc.)
-One font to rule them all!
-No option to use your favourite sites' favicons. You have to use generic ones, can't even import your own.
-Favourites can't be added as clickable snapshots, arrangeable in a grid.
-Adding these favourites is a bit ardous.
-No 'Export Settings' feature.
And there's more that (at least to my mind) is lacking. But the extension is relatively new and does what it says for free = 4 stars.
Deeper customization options, a less rudimentary UI for said customization = 5 Stars.