buying one
As others have said you have to ride one - but when did you ever buy a bike without riding it? So assuming you liked the test - what are the things that might irritate you if you own one? The gear change is pretty crap really but mine (2001) has improved with age and definitely with the addition of synthetic gear oil. It's simply worse that other shaft driven bikes (Japs and Italian) and much worse than chain driven bikes with good gearboxes. But it's bearable - it depends how much mechnical clunks worry you. I suppose the point is that you have to think a bit about the gear change to get it right (silent) and you shouldn't have to.
The lights aren't great either and lots of people end up with higher power bulbs and /or additional lights. The GS is not alone in this but it suffers from two things out of the box. One the dip/main arrangement leaves you with a single dipped beam - many others have two of course and if you are used to a twin headlight set up the GS mono arrangement is poor. This is especially true if you ride in winter when with a dirty headlight (yes yes I know I should keep stopping to clean it) and the brightness of car headlights - it can be challenging. The other thing is that becasue of the height of the thing if you are going for it on a road you know at night you'll find the dipped beam just not covering enough road. Solution? Add lights.
Suspension - I found the standard set up harsh - Ohlins front and rear have made a big difference. I suppose the point was that I felt the units needed changing but it's a very subjective thing suspension - depends on your riding style and weight, of course and what roadholding v comfort trade off you want. This was harshness over pot holed and poorly repaired town and country roads - not at 50-90 on A roads.
Screen - a lot has been written about the screens. Aagin it depends on your height and helmet and what you are used to. But I've had to fit after market screens to other bikes so it's par for the course, I guess. But I didn't actually get high speed cruising right until I put a higher screen on, Tobinators and took the beak off. Now I get pretty still air with minimal buffeting at 100 mph+.
There are other details - like front fork corrision - but all bikes corrode - if you use them in the winter, as I do - even with a good coat of wax.
So - why persevere with it? Well they are just bloody good bikes. Not all the faults = 'character' but the basic dynamics of the bike are good - handling, braking, road holding, smoothness, economy, road presence - they all get good to high marks. I am equally happy blasting down the motorway, exploring B roads or going too fast down well surfaced A roads - plus getting the shopping on it. And compared with my last high mileage bike (first series Triumph Sprint) it needs no TLC apart from cleaning and servicing. The Triumph was hungry for chains, sprockets, fork oil seals, headlamp bulbs etc etc.