Knocked out every SRIV: Re-elected trophy except for the 40 hours of playtime, so that's idling now. I can definitely see why people think it's more an expansion on SR3 than its own game even though I haven't played SR3; SR4 has no story at all. Plenty of activities, collectibles, and quests for each character, but without a story the game felt very lacking. The activities tended towards feeling tedious, too, and the sense of progression stops halfway through the game because hitting the level cap comes really really early.
Poor trophy list IMO. The weapon kill challenges and super power kill challenges just felt like a chore rather than stuff you picked up naturally. Upgrading the weapons before doing each related challenge is definitely a good idea due to how long the base form of each gun takes to rack up kills.
I noticed somebody else was playing SRIV but can't recall who. When you get to the Enter the Dominatrix level make sure you have the disintegrater and thumper weapons maxed out. There's trophy for killing all the other carts in a race that is impossible to get without upgraded weapons.
I'm definitely going to wait a while to play Gat Out of Hell.