I love how you're not picking so-called 'classic' episodes but slightly less remembered ones that still contain all of the great aspects of a show. And I very much approve of your picks for DS9, B5 and Merlin. In the case of B5, I probably would name 'Fall of Centauri Prime' as my favorite (because I'm a sucker for heartbreak, natch :) ) but when it comes to picking an episode to re-watch after not having seen anything of the show for some time, 'Dust to Dust' is on top of my list as well, for all of the reasons you mention!