I don't normally comment on pop culture, but this is worth noting.
It takes a Charlie Sheen type of guy to play the Charlie Harper type of humor. It seems to me that Ashton Kutcher is not a Sheen type of guy. If you like 2 and a half men, prepare for a different type of humor that's either mediocre or overused, or poorly delivered Sheen type of humor.
My prediction is that the new 2 and a half men is sadly not going to retain its former glory.