Absolutely nothing.
I love this motorcycle. It has more than enough acceleration to get you into, or keep you out of trouble.
It's not a sport bike.
It does have decent handling in the twisties.
I have put 35,000 miles on this bike in 19 months.
It still performs flawlessly.
I am 5'10" and have had NO problems with the seat. I routinely put 200 miles without stopping. I think it's very comfortable.
The motorcycle stands out in the crowd by its look. I'm always told by passers by how nice it looks.
My only change would be dual disk brakes in the front and a single disk in the back. However the stopping ability is adequate.
It gets 55-60 miles per gallon.
I agree with your comment about the disk brakes. It seems to me that Suzuki cut corners on that. I found that after I added a set of Hard Krome Exhausts and a Power Commander that the bike woke up a lot, it's even better in the twisties, and it really gets up and goes, still isn't a sport bike though.
A bit of advice to Suzuki... add that tacho and a fuel gauge.