Here's the deal... in my opinion. I think the A5 is actually living very well up to it's reputation as grand tourer:
- The car is actually as wide as an A6 (well, one millimeter less), and wider than an A4 B8, giving people sitting in the front a bit more breathing room on the sides and the massive doors won't come at the cost of space in front. This car will absolutely seat two adults (of practically any size) for any trip, be it to the grocery store or cross country.
- Its trunk matches the size of the larger A4 B8 (same dimensions except in height, but still, a very large trunk - larger than say A4 B6). This car will haul your daily stuff, but also your travelling gear. Comparisons to the A3 above show just how tiny the A3 trunk is compared to an A5 (although of course the A3 benefits from the wagon-like configurability).
The above attributes actually place it in competition with larger sedans, in my book. A4 B8, A6, VW Passat etc. are (by European standard anyway) quite large sedans and A5 has the ability to compete with them...
...in everything else but the rear seat space. This is where the compromise comes from that allows A6-like front space and A4 B8 -like trunk in a sporty car of only 4.6 meters long. Add to that the sloping roof-line, which is absolutely gorgeus design-wise, but terrible for the tall person sitting in the rear. (Not as bad as an Audi TT trunk door that would actually hit you in the head, but bad nevertheless.)
The A5 is a large, beautiful car that in my opinion pretty much comes at only the cost of the rear seat comfort, nothing more. Don't expect miracles for the rear. Otherwise this actually seems like a very sedan-like, versatile car when it comes to usability. And the looks win any sedan in spades, of course.
If your requirements for the rear are reasonable, say, one or two younger kids (that don't require massive back-facing-front Isofix/Latch seats or something), you'll have a very good everyday car in the A5/S5.
I wonder if a daily experience with this car would confirm my opinion, but so far this is how I see it. Feel free to comment.