Here’s a hack you can use.
Update: As Andrew Bartel mentioned below. It’s best to copy the template files into your theme so that they override the default woo commerce template files.
In your woocommerce plugin folder, look for a file called product-reviews.php
woocommerce/templates/single-product-reviews.php
Look for a line that says
<div id="review_form_wrapper">
Either remove the class review_form_wrapper, or add a 1 in front of it. That will make the hidden form visible.
Next you will want to remove the other buttons that says ADD REVIEW (triggers lightbox), because you will already have the SUBMIT REVIEW button at the end.
You will want to modify these lines to your needs:
<a href="#review_form" class="inline show_review_form">submit yours</a>
<a href="#review_form" class="inline show_review_form button" title="' . __( 'Add Your Review', 'woocommerce' ) . '">' . __( 'Add Review', 'woocommerce' ) . '</a>
You could either remove the lines above, or you could just add a display:none to each paragraph element to hide the whole thing
style="display:none"