DRK is pretty boring until 70. It used to be really fun to play at 60 in HW, but they took away a lot from it I feel. It's even more mundane below 60. Being able to spam TBN, Quietwhatever, and Abyssal drain on mobs at 70 is quite satisfying on the flipside.

NIN is NIN, at whatever level. Probably the least affected class by the 4.0 changes, and it feels just as enjoyable at every level 50 onward.

SMN is probably the one class that sticks out for dramatically changing when you get DWT. It's utterly boring before then.