A quick review of last night's "The Big Bang Theory" coming up just as soon as I understand why America has struggled to adopt the metric system...

"Big Bang Theory" is the most popular comedy on TV, and one I often enjoy quite a bit, but it's had varying tone issues for a lot of its run. In the early days, the show couldn't decide whether it was laughing with or at the nerds, before wisely landing on "with." In more recent years, especially as the show in general and Sheldon in particular have grown so popular, the writers can't always decide where to draw the line for what behavior of Sheldon's would actually be tolerated by the rest of the group, and also how much any of these people — whether friends, romantic partners, and however you choose to define Sheldon and Amy — actually like one another. Most sitcoms, especially traditional multi-cam ones like "BBT," depend on viewers wanting to spend time with these people every week, and there have been episodes where I haven't wanted to hang out with the group any more than they seemed to want to hang out with each other.

Last night's "The Romance Resonance" was, thankfully, not an episode like that. Though Sheldon was relentlessly smug about his discovery for the first half, it was coming from an understandable place, and his self-loathing upon realizing his error gave Jim Parsons a lot of terrific material to play. Parsons is great no matter what you give him, but Sheldon needs to be vulnerable like this from time to time to leaven the other stories where he's operating from a position of inflexible, destructive superiority.

And the two romantic storylines were both a lot of fun. For the most part, the show operates under the default philosophy that Leonard is incredibly lucky to be dating Penny. And while she's had to change herself a lot more than he has to make their relationship work, it was nice — and funny — to get a story reminding her why she's pretty lucky, too, and one that ended in such a warm, genuine place as the scene where she showed him all the mementos of him she kept in a box. "BBT" will occasionally sacrifice characterization for the sake of a good joke; this was a story that had plenty of jokes while letting the characters be people.

And Howard's song — written by former "BBT" guests Riki Lindhome and Kate Micucci (aka the musical comedy duo Garfunkel & Oates) — was just a treat: clever and nerdy and entirely heartfelt. Wolowitz at times is written as such a goon that it makes you wonder why Bernadette would have stuck with him, but Simon Helberg and Melissa Rauch played that scene (embedded below) as two people whose love was real and palpable, regardless of whatever stupid things Howard will say and do in the next three episodes.

In all, that was one of the show's strongest episodes in recent memory. Balance is a tough thing in comedy, and a lot of TV's best sitcoms this fall have had issues keeping all their elements in check. But when you get a half-hour like this where everything's working in harmony, it's a real pleasure.

What did everybody else think?