Is this game closer to DA:O or the older D&D games BG series, Icewind dale etc ?

I've seen some strong criticisms of this game, but mostly it has due to bugs which I'm guessing have been mostly fixed by now right:?

Neither. But if I was forced to choose, it would definitely be closer to DA:0, but don't compare them.

For me, the very worst criticism of NWN2, without question, is the camera. I don't know what they were thinking!

Rules-wise, the BG/IWD series (in particular IWD2 which first implemented 3rd edition AD&D rules).

Graphics-wise DA:O, but NWN2's lighting is far better (in particular it has a day/night cycle with shadows updated as the sun/moon crosses the sky). This does make it more demanding CPU/GPU-wise than DA:O though.

Bug-wise, most have been fixed but there are still glitches in the main campaign with some scripts/cutscenes not always firing properly (which can break games). Keep multiple savepoints so you don't have to restart should it happen to you.