It's not fair to a) compare this show with the original Charmed series or b) make an assessment of how good it is from only three episodes.
But I'm going to do both.
First, I will say that I never would have even tried this show if I hadn't been a fan of the original. CW shows are inevitably "not my cup of tea". I'm too old and traditional for most of them. This show is no exception. It's "young" and "modern", and I am not. It's "dark" and I like "light."
This show can't decide if it wants to be a comedy, a drama, or a superhero comic book. The original show was all three; this one is none of the three. The comedy generally falls completely flat, the drama is pedantic and unbelievable, and the characters are not likeable at all. The scripts are horrible, and, at least so far, the storylines have been boring.
The worst thing about it is that the relationship between the sisters is not what it should be. Here is where I definitely compare with the original show. The most important thing in the original was the unbreakable bond between sisters; miraculously that show made that work, not once, but twice, when the bond was broken by death and had to be reestablished with a new sister. The new show can't even establish any chemistry between the two sisters who were raised together, much less the interloper who comes knocking at the door one day. They pretend the bond is there, but it is clear to the watcher that it is not.
I'll probably keep watching for awhile, to see if it gets better. But I'm not convinced it will.