1. is it worth the high price tag?
2. are there other prime lenses you like better?
3. is it better than zeiss prime ze series?
I'm still using the MkI - it is by far my most used wide-angle, and I use it wide-open an awful lot. But to answer your qusetions:
1. Depends on whether you need such a fast wide-angle. Given that (I assume) the MkI will be discontinued, then if you do, it must be!
2. No, nothing else is so wide or so fast for Canon. At some point I will look at, and if I like it, I will buy the MkII - whether I do will purely depend on its wide open performance.
3. As far as I am aware Zeiss don't make a 24/1.4 so they make nothing comparable.
If you are talking about performance levels at other apertures, then I'd suggest that there are an awful lot of options depending on whether distortion is a big deal or not and at what apertures you need it to perform.