OK
Most of the changes are visual changes, rather than functional changes. Below I have summarised the changes I've noticed so far. (Australian Data & Metric units mentioned):
Version 26
- Shows as 4-1/60 on the Settings Screen
Display
- Boot up ==BMW== slightly different ('better' shades of grey). Not obviously different really...
- Antialiased display (no longer 'blocky') with smooth scrolling

- Colouring improved (water, forests, roads, etc - better contrast & clearer)
- Car 'icon' now clearer (white ring, with blue triangle, with shadow)
- Destination icon is a Chequered Flag
- POI icons are greyscale in white boxes (much cleaner icon design)
- 'City Centre' or 'Suburb Centre' icons are now small grey targets which are more subtle
- Major road labels are more accurate now (M3 instead of 3, for example)
- Use of subtle shadows (road labels, POI icons, car icon)
- Street names are easier to read, but only show at scales of 200m or less
- Landmarks (parks, etc) have a font which looks embossed.
- When zoomed out, cities are labeled with small square next to the name (see images).
- 'Direction of Travel' viewing mode:
- car icon is fixed in its position on the monitor and the map rotates
- rotation is fairly quick and smooth, particularly at lower scales
- this works even when zoomed out to 200km, above which it reverts to a 'North Orientated' view
Function
- POI Icons appear at larger scales (start to be seen at 5km scale cf 2km)
- POI Icons can be switched off (Function under 'Information - General Destinations' called 'Disable Icons')
- When a POI is selected as a destination its icon is replaced by the flag icon
- Route List shows list to the destination even if guidance never started and it updates on the fly.
Minor Glitches
- Some roads & map items appear to not draw properly (can be fixed by just zooming out and back in again).
- Destination Input Map:
- Scrolling is faster but quite jerky
- Smaller Roads (the brown ones) don't show at a scale of 500m (have to be 200m or less, unlike the old system).
- At scales of 1km or less, the 'smaller' yellow roads do not appear unlike the old system
Other
- Accept Screen still gone

- Split-screen for the radio still works.
That's about all that I've noticed so far. I hope this is of some use.
Cheers,
Paul Martin
Australia