The C in CRPG stands for “computer”, and was originally meant to differentiate them from pencil and paper RPGs, like D&D. That is to say they try to mimic what it is like to play D&D style games, with the openness and freedom that entails.

Obviously that is impossible, since in D&D you can do anything you can imagine and describe, provided it fits in the rule framework and the DM plays along. Including, if the DM is willing, just running away from the story to do something else entirely. But CRPGs usually try to let you have multiple ways to solve the problem of the moment.

There’s also a big emphasis on story, and very often quests will be delivered narratively. As in, if you wander into a town you might talk to someone who mentions they have a problem and then it’s just kind of… up to you to decide how to help? If you’ll help? You don’t tend to get a marker on your map and a note in your journal to go kill 5 rats, for example.

Also combat is often turn based and you usually control a whole party. So in short it’s not like Diablo really.