Owned a 650r since 2006. Been riding since 1990.
The 650 has a parallel twin engine. It sounds nice, but will not sound like a cbr or comparable sports bike, even if you mod it. It's considered a sports-tourer. At high rpm's with an airfilter mod it will sound nice though. But you won't hear one of these revving to redline, half a mile away at night.
The rider position is more upright than a true sportsbike, so unless you swap the bars out you won't be lying on the tank when you ride. Much more comfortable if you decide to take a ride more than an hour, but it doesn't look as "cool", especially if you have a passenger on back.
In the twisties, I can keep up with just about any sports bike out there. This bike handles very well and is quite forgiving.
This bike does well on straight-aways but after a certain speed, other bikes will overtake you easily. I will say that the torque curve on the bike is nice. Also, I don't even need to leave 1st gear (if I don't want to) unless I hop on a highway. Other bikes have to toss a shift or 3 in there.
All this being said, it's generally considered a decent beginner bike. I've had faster and slower bikes. But I'm not getting any younger nor can I afford any more tickets... so I'm holding onto it.