There are some phenomenal pieces on display from unknown, new artists. If you are going expecting to see a lot of the modern "classics" or more established, big name artists, you'll be disappointed in the SFMOMA. If you want to gain exposure to new and exciting artists, this is the place to do it. The layout of this museum is a little confusing and the atmosphere is cold and unpleasant. Modern doesn't have to mean lifeless. The galleries are nice with well presented information and lots of seating for lengthy contemplation.
The rooftop patio is a nice place to chill but watch out in the cafeteria -- they have signs all over saying "no outside food and drink" and they mean it. I had a low carb protein bar in my bag and I took it out to munch on (I purchased a coffee at the cafeteria) and not two seconds after I opened the wrapper, a security guard with a very nasty attitude came over to chastise me for bringing food in the museum. I hadn't even take a BITE of my snack and she went what could nearly be described as "nucking futs." I ended up going in the bathroom and eating my snack in there. I purchased a drink there but I need a sugar free / low carb snack option and the museum cafe offered nothing that would work with my dietary restrictions.
The museum is close enough to a BART station, making it easy to get in and out of the city. It's only a couple of blocks walking distance.