It took me around 6-7 hours. I was taking my time. I agree, the puzzles could have been harder. The puzzles in Portal 1 were more creative. Often you would do one part then another and then you would figure out that this isn't the full solution yet while here they were usually straightforward. I got a bit stuck only a few times, but I figured it out quickly.
Dialogue-wise and story-wise more entertaining than the first one. xD Also, the last boss was way too easy.