I've owned two E53's and I currently own an E70. I loved my E53's and don't find the driving experience to be significantly different with the E70. I bought the E70 as I wanted a later model vehicle with more of the bells and whistles.

From a maintenance / repair perspective I really can't speak. My E70 just broke 50K miles and, aside from an unusual seal leak in the front drive train, it has been trouble free. However I don't do any maintenance / repair myself...I have my indy mechanic do it. He states the E70 model isn't any more difficult to work on than the E53 though he specializes in BMW's and therefore has all the necessary equipment to work on them.

The one thing I really miss from my E53 is the sunglasses compartment...I know...silly.