This is a cool episode, not just because it is the first regeneration (although that sequence is quite interesting).  What really stands out here is how well and realized the Cybermen are.  Sure, they come across as a bit goofy, but they are also brought along with a certain sense of dread, and they nicely do the sci-fi thing of exemplifying fears and concerns about humans elective-surgery-ing themselves into monsters.  I found it pretty fascinating overall, even in things did get a little shouty near the end.  It's a bittersweet kind of story in that it is sad so see Hartnell go, but you can tell his health problems were getting to him and you can't help but mourn him a bit while watching these episodes.  An easy story to identify as much-watch in the world of Doctor Who, even if the last episode is tragically missing.