MF lenses are design to cover a larger area (duh). As for the differences, I wouldn't know, but I guess it'll be like the same as with any piece of equipment.. There'll be the really good ones, and the really shite ones.
Technically, MF lenses can be manufactured to deliver lower resolution compared to equivalent 35mm lenses since they project an image on to a much larger area of film. Hence... they can record more overall detail even though they are usually not as good as 35mm lenses when you compare 1 sq-cm of a MF neg to a 35mm neg.
If you're talking MTF, highly regarded 35mm lenses (primes, macro lenses, etc) usually rate as high as 4.6-4.8 but MF lenses typically rate around 3.2-3.8. Yet, they deliver the goods (better than 35mm) due to the large film size.
This is one reason why you can get cheap large format lenses for a couple of hundred dollars which can squish any 35mm outfit with your expensive 2000 dollar lens.