With a party size of just 4, you need to have those traditional Rogue utility skills more available to the rest of the group. As someone who almost always plays a Rogue, I don't mind that. There is still plenty of fun to be had in the Scout and Sneak Assassin role. It's like healing, a point made previously. With just 4 in the party, you don't want to be forced to take a dedicated healer.
Once a fight begins, I'm the one moving around the most, looking for opportunities to sneak attack with bow or blades while the rest of the party is engaged in direct combat. I don't feel that any other class is really set up optimally for that, so playing a Rogue still feels like a unique class to me.
