I was actually very disappointed in SR3. there's nothing "added" only replaced. the "new" activities (which are just variants of older ones) replace some of my favorite ones, like crowd control and fight club. The customization is certainly lacking compared to SR2. There's Planet Saints which you can look like your average teenager attempting to get into a party, then theres maybe one or two other stores and they have almost no items. I ended up going with a simmilar path to Yahtzee in that I had a nicely dressed man in a pin striped suit and a top hat tilted at an absurd angle which contrasted nicely with the maniacal killings I did back in SR2. In Saints Row the Third, I can't choose to make my suit a pinstripe, and I can't get my hat to fit any other place than squarely on my head.
If it wasn't for the streets of Steelport feeling more lively than sr2's did, I would say that this game was a complete downgrade. I mean, after my first playthrough of 2, I had logged 20 hours. after beating the final mission in 3 it was up to 9. You can still get much more out of it, just like 2, but it really ISN'T as much fun. I literally went back saints row 2 and restarted the story another time (by now I have over 100 hours, not including times I didn't save by the end) and I haven't even beaten the Ronin missions yet. (i'm about 1/3 done with the game for those that don't know) Also the headset from the premium pack isn't very special. The autotuning is pretty lame and it isn't the highest end sound for something in it's price range.
BTW, that part about not having any introduction to the activities is false; they just put it in as the missions. For example, Professor Genki's S.E.R.C. is because Pierce put you in the show as a contestant to earn money.