My first BMW experience was upgrading my wife from a 2011 Mini Countryman to a 2012 X3 in early summer. (I did spend some time driving a 1992 BMW 325is and helped a friend restore a 2002tii in the 90s.)
Later this summer when looking at late model Boxsters (I've owned several Porsches), I learned of the great model-year-end lease deals on the 2012 Z4. I took the bait and now we're having fun with two new BMWs in the family.
Normally I prefer sports cars that are a little sharper (more involving) than the Z4, but it'll be fun to spend a few years with it and see what's available in 2015 (new Z4, Boxster update, 911) when the lease is up.
I'm planning on upgrading the exhaust (If we ever get some good choices for the N20!), but probably purchasing a ECM tuning box first.
The Z4 IS a very pretty car.