what was the surprise?
You likely aren't going to really appreciate the difference in a mere 8x10" print, but enlarge to 16x20 and larger and the difference becomes quite obvious!
Since the same subject covers more film area on a larger format, you have less graininess, better tonal gradation and color gradation visible from medium format when viewed at the same final size.
I once was enrolled in a workshop at the local community college, and we would have slide viewings of three shots from each class member. I shot in medium format, and the ooh's and ahh's from the class were notable when my slides were projected because of reduced graininess and better tonal and color representation, and the instructor (who was a contemporary of Ansel Adams) used that as an opportunity to tell the class about the reasons for the visual impact of the larger format.
the bigger negative is easier to retouch -- mask, etc.
Negative real estate is the main factor.. how much information you can cram in a given amount of space that will transalte into details.
I shoot both 35mm and medium format. For me, the larger the format the slower I work. So this is one aspect. As for print quality, the pay off is when you print larger than 8x10. I made an 8x10 print from my 35mm neg of Ankor Wat in Cambodia. I have a tough time distinguishing the quality some shots I made with my 120 camera. I shot 35mm Fuji Acros souped in Xtol. My Canon F1 I feel the most comfortable with and I tend to shoot more film than my Zeiss Super Ikonta IV.