I picked up my copy of the 5th edition only very recently, because I had stopped playing 40K for a while due to other things in my life. Read the whole thing front to back in a few hours, and I'm pretty sure I figured in all the new bits that were changed from 4th ed.
Can't really say yet if I like the new rules more than the old ones yet, haven't played all that much yet, some of it is good, some of it 'makes sense', other bits are a bit annoying. ( like no longer having automatic penetrating hits with my melta's or excorcist, this makes having to resort to inducted guard for some much needed lascannons almost a must have for WH. Or getting a landraider ( or both ;) )