It depends on your team. If you have good juniors, they will relish the feedback. Of course it needs to be substantive. Often junior code will be far more complex and difficult to read than senior code, and code reviews are a chance to get that feedback across.

That said, often teams don't give credit for code reviews, or take into account the (sometimes considerable) time required to write them. To some extent, tools are also to blame - I think all teams would do well to pick a system that integrates with the dominant IDE. Doing code reviews in the same space you write code just makes sense; requiring that you use a friggin' webapp is HORRIBLE.