It's also worth remembering that IWD2 is as much a puzzle game as it is a combat game. It's mostly remembered as a combat game because the 2nd section of the game is quite a long drive through reams of Orcs on your way to the Orc Castle. However, it's normally the puzzling aspect which gets to most people, either positively or negatively, what with there being no end of really, really good cRPG puzzles.
Even if you OP all the combat to insignificance, the puzzles will still be just as hard as if you had a regular party. Off the top of my head there's the Bridge Dynamite timed puzzle, navigating Fell Wood, the Time Travel story game, the Ice Temple Alternate Plains, the Seven Monk Trials, Summoning The Guardian, and likely many more that have briefly escaped my memory.
Now, I'm not a great fan of puzzles, especially Adventure Game puzzles like Slidey Puzzles, Combining Items, Pixel Hunting etc, but these aren't those types of puzzles, these are all genuinely good cRPG 'proper' puzzles, the kind that blend perfectly with D&D type adventures. If there's one thing modern games players and developers could benefit from taking from IWD2 it's the puzzle implementation IMO. Many are, without any doubt from me, some of the best cRPG puzzling I've ever enjoyed.
As an example, here's a spoiler heavy guide-map to the Fell Wood I drew up once, do not open if you want to work out Fell Wood for yourself, feel free to download and keep if you want for future games:
What other cRPGs of the post-Wizardry era would require a map like that for one of its stages!