Sony kept improving size and weight. E35 is much smaller and lighter than E2. Anyway, even E2 with it's size and weight is still acceptable. Good thing is that newer units have backlit on the LCD, which is very comfortable. Both E35 and E2 don't have backlit.
Last thing is the design.
I think design of the E2 is great even though it's made of plastic. I can hardly accept design of E35. Back side of the unit is very ugly and keys are so small an put so close together that it is difficult to use them. Remote is very bulky and looks unattractive. I hope Sony will keep this tradition.