If I can play only one from three what it should be?
I read from CRPG book that the third one is a disappointment but I don't see anyone who doesn't like it.
So what game should I play? I don't believe I will go through all 3.

If I would have to choose I take the second part. This is one with which I started and love most. But, anyway, I like the whole series a lot. :-) The issue is that the Ishars were mostly accepted in Europe, in USA they didn't catch the a big number of people.