Rogue Trader Space Marines were a lot less cool. They weren't giants, demigods or warrior monks, they were shown getting absolutely slaughtered a lot more often than now, and were often depicted as gross, decrepit old men technologically sustained way past their time–a walking gerontocracy.

(I alt-texted Raven Guard even though Dark Angels is right there on the guy's pauldron. Dumbass.)

If I'm not mistaken, this is the first ever depiction of the Emperor. You definitely got the sense of the Imperium as a decaying, sclerotic empire more than the Indomitus Crusade stuff of the current edition gives you.