Can´t say I have a clear preference, what´s most important to me is that interactive features a game devotes majority of playtime to are fun to engage with on a minute to minute basis.
Among some other things, this means
a) I don´t care much about how good stuff is "on paper", it´s how it´s utilized in practice what counts - combat system doesn´t mean much without encounter design, story doesn´t mean much without allowing for ways to interact with it, character system doesn´t mean much without appropriate opportunities to apply it on, etc.
b) weak features don´t phase me much if they consume proportionately low amount of playtime and a game makes up for them elsewhere
c) setting and art direction are always important to me due to their omnipresence during a playthrough, but they´re not
that important due to their non-interactive nature
Well, if there´s one feature that I´d name as the most important one, for me it would be reactivity, meaning the ability to change course of a game based on how I defined and/or express my character(s).
On a very general level, this mostly means allocation of stats opening new play styles/ ways to overcome combat and other non-narrative obstacles, or ways to alter narratives via dialogue choices or other actions.
Meaningful reactivity for me means it simply leads to fun results, the changes don´t have to be big all the time
.
I guess another way to characterize this might be depth of interactivity, including that between different game systems.
Therefore I went with choices & consequences, with the above take on the feature in mind, though I also agree with this:
None of these things stand on their own. Without a blend of at least 3 or 4 good ones no cRPG is going to be worth the time to play it.