Marvel's Agents of S.H.I.E.L.D. ratings fell despite a big Captain America: The Winter Soldier crossover. Credit: Disney/ABC.

Wow. Just...wow.

Don't worry. I'm not going to spoil last night's episode of Disney (DIS 0.56%) Marvel's Agents of S.H.I.E.L.D. for you, but I admit I never saw it coming. Thanks to a massive planned crossover with Captain America: The Winter Soldier, I say that as a fan who was fully expecting big changes and shocking reveals from the ABC drama going in.

But we were in for another surprise this morning: Preliminary ratings for last night's episode actually dropped by three tenths from last week to a season-low 1.7 in adults 18-49. Agents of S.H.I.E.L.D.'s estimated live viewers also fell by roughly 800,000 over the same period to just 4.91 million. 

Meanwhile, and despite winning its second Tuesday in a row, Comcast (CMCSA 2.96%) NBC's The Voice also fell by two-tenths to give it a 2.8 rating with a live audience of 11.76 million. The lone gainer was CBS' (PARA -0.92%) NCIS, which enjoyed a 3-tenths of a point bump from last week's final numbers. That left CBS' typical ratings juggernaut a close-second with a 2.6 rating and 17.18 million viewers.

Don't give up on S.H.I.E.L.D. yet
But before you lead Agents of S.H.I.E.L.D. away in cuffs, some perspective is in order.

Keep in mind these are preliminary Fast Affiliate numbers, and Agents of S.H.I.E.L.D. has made a habit of fooling industry pundits with upward adjustments when the final Tuesday figures are revealed two days later. When all was said and done six days ago, Agents of S.H.I.E.L.D.'s ratings and live viewers for last week's original telecast were increased by two-tenths and 320,000 people, respectively, resulting in its final 2.0 for adults 18-49 on 5.71 million viewers.

In fact, 13 of its 17 original episodes have gone up when the final ratings roll in -- twice by two-tenths including last week, and by one-tenth the remaining 11 times. Of course, this also means Agents of S.H.I.E.L.D. will need to see its first ever three-tenths upward adjustment in order to match last week's final rating. I'm a stubborn optimist, but even I'll admit that seems unlikely.

Even so, this doesn't mean Disney is about to drop the axe, especially after ABC chimed in this morning to say Agents of S.H.I.E.L.D. just won its hour with Men 18-34 for the 17th consecutive episode. In addition, S.H.I.E.L.D. remains tied as the season's top-rated broadcast drama overall with Comcast NBC's The Blacklist.

Finally, with 63,826 total related tweets yesterday -- a 124% increase from last week -- ABC states Agents of S.H.I.E.L.D. was Tuesday's "No. 1 most social primetime series across cable and broadcast." Sure, that's admittedly a less conventional metric for measuring its worth, but I'm still convinced Agents of S.H.I.E.L.D.'s strong social media presence remains one of the most effective drivers of its long-term success.