public function reviewAction()
{

}

<layout>
        <updates>
            <mcreview>
                <file>mcreview.xml</file>
            </mcreview>
        </updates>
    </layout>

<mcreview_index_review>
    <reference name="root">
        <action method="setTemplate"><template>page/1column.phtml</template></action>
    </reference>
    <reference name="content">
        <block type="mcreview/data" name="magecomp.mcreview.data" template="mcreview/review.phtml" />
    </reference>
</mcreview_index_review>

public function reviewAction()
  {
     $block = $this->getLayout()->createBlock('core/template')
      ->setTemplate('mcreview/review.phtml');
    $this->getResponse()->setBody($block->toHtml());
    $this->loadLayout();
    $this->renderLayout();
  }

public function reviewAction()
  {
    $this->loadLayout();
    $this->renderLayout();
  }

<block type="core/template" name="magecomp.mcreview.data" template="mcreview/review.phtml" />

public function reviewAction()
{
    $this->loadLayout();
    $this->renderLayout();
}

public function reviewAction()
{
    $this->loadLayout();
    $block = $this->getLayout()->createBlock('Mage_Core_Block_Template', 'block_name1')->setTemplate('mcreview/review.phtml');
    $this->getLayout()->getBlock('content')->append($block);
    $this->renderLayout();
}

public function reviewAction()
{
    $this->loadLayout();
    $this->renderLayout();
}

<mcreview_index_review>
    <reference name="root">
        <action method="setTemplate"><template>page/1column.phtml</template></action>
        <block type="mcreview/data" name="magecomp.mcreview.data" template="mcreview/review.phtml" />
    </reference>
</mcreview_index_review>

<?php echo $this->getBlockHtml('magecomp.mcreview.data'); ?>