I too understand that some people like the newish "checklist" behavior. But many of us do not. There is no reason that they could not co-exist.
HOWEVER, many of the comments in this thread are entirely missing the points which trouble me. Sequences of checkboxes in people's lists should:
NEVER be automatically converted to a checklist. It is simple enough to highlight and change to a checklist if desired. But the frustration we all feel when you inadvertently hit enter to insert a new checkbox-prefixed item and the entire note turns into a checklist is quite a poor design choice. If you haven't suffered this, please try it with an open mind and you'll see what we mean.
Who really thinks that manually adding <space>[]<space> before every item that you add is user friendly? I totally get that this is fine for adding multiple checkboxes in a row in a table or something... but it is clunky and clumsy to do this on each a new line. It shouldn't be so hard and clunky to maintain the behavior we have become used to for years,
What is wrong with the following behavior:
Hitting <Enter> in a checklist adds a new checklist item
Hitting <Enter> at the end of a line preceded with a checkbox adds a new line preceded by a checkbox (the way this USED to work before v10)
As a long-time UI designer, I am very sensitive to forced paradigm-shifts. The Evernote staff that created this bifurcation clearly favor the checklist style of behavior (strike-through and graying) for their lists. I have no problem with that, and might even use it for some "one and done" types of lists. But there are a lot of us who have depended on an established behavior and it has been made incredibly cumbersome for no apparent reason other than to deprecate checkboxes to special-case usages such as when used in groups.