It seems to me that roleplaying has two basic meanings for an approach to playing BG:EE.
One is the traditional sense from tabletop gaming to immerse oneself in the character, and imagine what the experience is like. In BG:EE this may or may not be brought to life through journaling. But in either case the player puts him or herself in the shoes of the character.
And mind you, this can be done not just for the PC--but also for all the party members!
The other sense of the term "roleplaying" is predominantly tactical. Here the emphasis is simply on behaving in-game strictly according to alignment, class/kit, backstory, and only what the character can reasonably know of his or her world
. This is less intensive work imaginatively than immersion in the character, but it definitely shapes how the game goes.
Most importantly, this means no meta-gaming! For example, the PC (and party) has no idea where Bassilus is, so they don't just 'go get Ashideena'. And unless they send a stealthy scout ahead, the party doesn't know there's a band of Blacktalons lying in wait to ambush them ahead on the road. Similarly, they have no idea there's treasure in the knot of a tree. And it also means not rescuing a kitten for a little girl if you're the evilest sorcerer that ever walked the face of Faerun. Or if you're an Invoker not using a Wand of Sleep, Charm Person scrolls, and Algernon's Cloak.
I think it's fair to assume that players that do imaginative roleplaying typically also roleplay in the tactical sense of the term.
One place that both of these styles come together, I think, is when you roleplay NPCs also. And this sometimes can lead to surprising results, by the way, as you imagine relationships between them.
I've recently found that this approach to the game makes me feel like I'm actually on an adventure, versus just playing a computer game.
But anyway, thoughts?