version 1 doesn't have IS, is heavy, has a narrow focal length range, and is overly expensive.
version 2 doesn't have IS, has a narrow focal length range, and is ridiculously expensive.
24-105 f/4L IS is a much better value for money. Lighter, less expensive, better range, just as sharp.
If you need to shoot low light, use a prime lens. You could probably buy an "L" prime and the 24-105 for close to what the 24-70 v2 costs.
As you can tell, I am not a fan of these lenses, especially how Canon has priced them. If the version 2 had IS and was priced the same as version 1, I would would say it was a good lens for full frame. (I would still go for EF-S 17-55 f/2.8 IS for crop)
Some people love the current version of this lens, and can't wait for the new one to ship. I just think they are a terrible value for money.