Want to know the real deal?
No matter how great Cavill or the next actor of Superman are and how loyal are to canon (comics of course) it won't matter to some people, because they just want to see Reeve again and Donner Superman continuation disguised and have that on their minds.
Yeah as great as Reeve's performance was (Really good, I really love him), his Superman is nothing but another character interpretation. Same thing with CK. If those people don't see the clumsy Clark Kent (they won't, it's confirmed by Cavill) they will complain and say that wasn't Clark Kent no matter if in cannon he wasn't always like that or if it will claim more attention these times.
So yeah they will use any excuse, complain or critic to try to **** on his performance just because he isn't like they want to see (if they'd see it they will complain also: lack of originality, they just know to copy previous versions, blah blah blah) some just are for complain and I really DOUBT they fully enjoy a thing at all.
His Superman was a great INTERPRETATION of those times, and no matter if some people just can't deal with it, that version just won't click in these modern times.
We are for some realistic and canon inspired Superman now in the DCEU adjusted on these times. If they really want that version or a copycat of that, sorry but they are losing their time cause it won't be like that and character will still evolving as time is passing. If they can't move one they have 5 movies (SR was a homage of the Donnerverse) to watch the times they want.
/Rant finished