the original riven has a clever-if-you-get-it frustrating-if-you-don't out-of-the-box-thinking puzzle right off the bat that i have a lot of fondness for. it would definitely be hard to translate to the new "free movement" interface - it would require a lot of rethinking - so they basically ditched it.
it's not a bad decision, but i nevertheless mourn the loss of a very self-aware piece of adventure game puzzle design