I own one and it is great. It isn't overly slow but it is slow compared to most cars out there right now. Picked it for comfort really, the G35 seats annoyed me and the BMW 3-series just cost too much if I get the same features as what I have on the IS250. Great daily driver pretty much sums it up.
Outside of the numerous recalls, I go another one so it needs to be brought to the dealer again, it has been great.
Just keep up with the maintenance and this car will last a while.
I'm also a guy who gets tired of certain looks quick, I feel cars gets outdated easily but every time I step out of my house and see the IS250, it still looks great and doesn't look old or dated.