I went from a Mk3 Golf GTI to an A2 TDI 75, and I really liked it!
I wanted something seriously economical for the annual mileage I was planning to do, and I really struggled to get below 50mpg, and more often it was in the 55 to 60 region.
I liked the sound of the little 3 cylinder engine, kind of like half a V6!
The one thing I did criticise after 18 months and 45000 miles, were the seats and the ride with the 17inch wheels. Mine was an SE, and the seats were a little 'flat' and not very supportive around the thighs, and lateral support was nearly non existant. I felt like I was falling off them! I had a sport version as a courtesy car a couple of times, and that was much better. I thiught the driving position was good too.
The lack of a rear wiper was a bit of a pain, and visibility past the A pillar took a bit of getting used to, but no big deal. My in-laws used to have no trouble getting in and out of the back, and overall it was a pretty nice car. Never had to lay a finger on it other than maintenance.
Having said all that, my A3 after 90,000 miles has only ever needed maintenance as well (fingers crossed!), and I get between 47 and 50 mpg, so from a fuel saving point of view not a lot in it, considering my A3 has nearly twice the power of my old A2.
Mind you, at least the A2 was a 'proper' bespoke Audi, and not a re-bodied Golf. Not that there's anything wrong with that of course, but just that the A2 is a rather unique little car I think, and I certainly wouldn't complain if I had to have another one!