pro
The story of Saints Row 4 is fun and crazy, and will take you places you surely didn't expect. There is some solid writing behind the dialogue and jokes that makes the game pretty darn entertaining. It makes fun of a healthy amount of referential games, and keeps providing you with new powers and weapons throughout the adventure to keep you interested. Add in a self-aware Nolan North voice over (if you choose to) and you're set for a lot of craziness.
pro
Being in a simulation gives ample opportunity to provide you with some neat super powers. Except for a few activities where you steal cars, you will probably never set foot in a vehicle during the duration of the game. Simply running up walls with super speed and floating across the whole city will provide the best means of transportation. You will eventually get powers that can wipe whole city blocks clear of enemies, but being overpowered is some of the fun in Saints Row 4.
pro
With Mass Effect being only a fraction of all the games referenced, you will have loyalty missions for everyone in your crew. These are good solid missions with a healthy amount of fun sprinkled on them as well as fun rewards, like giving your crew their very own superpowers.
pro
Weapons galore! You might think that adding acid bullets to your gun would be a big change, but just wait until you point your gun at someone, watch their head inflate and proceed to blow up causing a chain reaction of other enemies blowing up too. Or maybe just lay down a beam of light that will suck your enemies up into the sky to a timely doom. If that's not enough, then how about a black hole gun that will not only suck enemies into its demise, but also vehicles and UFO's. Those are just a few examples of the big variety of guns you get your hands on, so there is no shortage of ways to get rid of your foes.
con
It's sad that all the fun I'm having is in such a dull looking city. Steelport isn't very exciting to look at or play in at all, as everything looks the same. The fact that you can't unlock daytime until you've finished the game means you're stuck in a dark, bland and boring Steelport for at least 10-20 hours depending how much you deviate from the main storyline.
con
Side activities have taken a huge dip in quality from SR3, and aren't nearly as fun as they were. Some old ones make their return but pretty much all the new ones are a waste of time.
con
... which makes the fact that 90% of all side missions are these activities. This is such a wasted opportunity and simply just lazy. Loyalty missions for the crew are the only proper side missions you will have.
con
SR4 was originally started as DLC for SR3 and in some ways it shows. There is no update in graphics, pretty much all the side missions are activities, and the lack of polish makes this feel like DLC instead of a proper sequel.
pro
Not only does it contain a great licensed soundtrack, but the use of some of the tracks during the game is simply amazing and hilarious. It's a great addition that you can actually listen to the radio outside of vehicles as well since you won't be spending any time in them.