If you have been in any of the competition over the last two years, I think "fine" is probably a kinder adjective to use. The design is unique, yes, but it also has that space eating plateau in the middle of the dash and the materials are quite poor. I would venture to say that a Camry XSE or Accord Touring have significantly nicer interiors. The C300 interior is beautiful and feels 2-3 classes above the IS, and the 3er is much nicer as well. I dislike the design of the A4 interior, but the materials are very nice. G70 interior is beautiful. This new IS has faux stitching across the dash, so that will hopefully go a ways towards improving the material of the glossy, 90s Toyota-ish dash material that exists now.
I can't put my finger on what should necessarily change outside of the shape of the IS' dash, but yeah... interior is a weak point for the IS, no way around it. That is why so many of us were expecting more of a change.
Keep in mind that we are talking about a car that's going to cost ~$55-60k for F Sport V6 trim. Hard to justify almost a 2x price increase over a Camry XSE V6 when they have the same engine and the Camry has a nicer interior, IMO. We are looking to move out of our IS 350 into something different, so this has been a point of discussion over the weekend.