WordPress Widget API vs Drupal 8 Block Plugin API

example-drupal-block.php

<?php

namespace Drupal\example_block\Plugin\Block;


use Drupal\Core\Block\BlockBase;
use Drupal\Core\Block\BlockPluginInterface;
use Drupal\Core\Form\FormStateInterface;


/**
 * Provides a Eventbrite attendees list Block.
 *
 * @Block(
 *   id = "example_block",
 *   admin_label = @Translation("My example block")
 * )
 */
class ExampleBlock extends BlockBase implements BlockPluginInterface
{
  /**
   * Return the block contents
   *
   * {@inheritdoc}
   */
  public function build()
  {
    $config = $this->getConfiguration();

    return [
      '#markup' => "Hello {$config['some_text']}"
    ];
  }

  /**
   * Return a Form API array
   *
   * {@inheritdoc}
   */
  public function blockForm($form, FormStateInterface $form_state)
  {
    $form = parent::blockForm($form, $form_state);

    $config = $this->getConfiguration();

    $form['some_text'] = [
      '#type' => 'textfield',
      '#title' => $this->t('Some Text'),
      '#default_value' => isset($config['some_text']) ? $config['some_text'] : 'Jonathan',
    ];

    return $form;
  }

  /**
   * Update the configuration values from the form state
   *
   * {@inheritdoc}
   */
  public function blockSubmit($form, FormStateInterface $form_state)
  {
    $this->configuration['some_text'] = $form_state->getValue('some_text');
  }
}

example-wordpress-widget.php

<?php

class ExampleWidget extends WP_Widget {

	/**
	 * ExampleWidget constructor.
	 */
	function __construct() {
		parent::__construct(
		// id_base
			'example_widget_id',
			// title
			__( 'My example widget' ),
			// widget options
			array(
				'classname'   => 'examplewidget',
				'description' => __( 'My example is great!' )
			)
		);
	}

	/**
	 * Echo the widget contents to the screen
	 *
	 * @param array $args
	 * @param array $instance
	 */
	function widget( $args, $instance ) {
		print "Hello {$instance['some_text']}";
	}

	/**
	 * Echo the widget form to the screen
	 *
	 * @param array $instance
	 */
	function form( $instance ) {
		$default_values = array(
			'some_text' => 'Jonathan',
		);

		$instance = wp_parse_args( $instance, $default_values );
		?>
        <label for="<?php print $this->get_field_id( 'some_text' ) ?>"><?php _e('Some Text') ?></label>
        <input type="text"
               id="<?php print $this->get_field_id( 'some_text' ) ?>"
               name="<?php print $this->get_field_name( 'some_text' ) ?>"
               value="<?php print esc_html( $instance['some_text'] ) ?>" />
		<?php
	}

	/**
	 * Sanitize a new instance array and return it
	 *
	 * @param array $new_instance
	 * @param array $old_instance
	 */
	function update( $new_instance, $old_instance ) {
		$instance['some_text'] = sanitize_text_field( $new_instance['some_text'] );
		return $instance;
	}
}