I've driven a lot of sports cars and this is among the most fun. I tried the M3/5 and the AMG and just preferred the way the IS-F is tuned. It is a lot more like a muscle car than the M's and I guess I'm just not a Mercedes guy. Plus, with Lexus, I don't have to worry about all the reliability issues of the Germans. Love the grunt, the automatic is buttery smooth and the manual mode is actually decent (from a diehard straight drive fan). Don't understand people whining about the ride. This is a SPORTS car, and it's actually not even that bad for a sports car. Plus I can get 25-27 easily on the highway, 28 if I try hard. Overall an awesome car. Would like ventilated seats, but small gripe.
Drivetrain is superb. Sound system good. Fuel economy awesome for what it is. I never see any on the road and, accordingly, this car gets tons of attention. Low profile enough, but mean looking enough to stand out.
Ventilated seats would be nice for us southerners. Maybe a HUD.