I've always liked the Impala - it's a solid mid-sized car at a good price. I haven't had a lot of seat time in the old car, but my father-in-law likes the ones he's rented quite a lot, and he drives an E34 525i, which is a wonderful driver's car, and about the same size.
Only thing I wish they'd done with the new Impala is to carry over the first-gen's round taillights. I think the new rear looks more generic. The front is okay, but could have stood a little more flash and dash.
LOVE the interior of this new car, though - big improvement over the old car. I like GM's new radios - lightyears better than that same old gray blobular Delco stereo they used to put in EVERYTHING.
Still haven't seen one in the flesh, though.