Dead Rising 2

First of all: There is a way to quickly level up for at least the first 25 levels.
I will split the guide of sorts in two parts.

*Start the game like normal.
*Dress as the ninja for stealth and not getting grabbed all of the time. (Rarely do zombies grab you, but it's 99% less than normal)
*Wear the Viking helmet of the fan outfit for walking a bit faster than normal.
*First save Denyce. But, it being the first scoop and somewhat of a tutorial on how to save survivors you have a bit of time to mind scoring some extra PP.

So: There we go hauling in those loads of PP (Beavis and Butthead laugh)

*Each time you give Katey a toy (see the Father of the Year and Father of the Month achievement guides for those which toys are wanted and where to find them) you get a ton of PP. It ranges from 5000 to 15.000 PP . For this moment we focus on all the toys you can get inside of the Royal Flush Plaza. Most stuffed animals are found there, just like the stick pony, the ball and a bag of marbles. Every time you have enough items, go to the Safe Room and give it to Katey. (Damaging the stuffed animals means Katey does not want them by the way!)

*You can earn a total of 9000PP in the sports shop in Royal Flush plaza. When walking in the plaza, you can pick a sledge hammer. Walk into the sport shop, press on the strongman game, which is 5000PP. After that, pick up either the MMA or the boxing gloves and punch the dummies until they break for 1000PP each.

*You can also earn PP in the Flaming Craps pen. Get rid of the three cops in the pen, and very simple: Throw a 7. (it already lays there a 2 times 6. So, take a dice and throw it right in front of you. Most of the time you throw a 1 and earn 10.000 PP)

*Next we can go to the sport shop opposite of the pen. Inside is a mini game which involves golfing and some timing. You give some money, press at the right time and earn up to 32.000PP if you win all three games. (First round is 1000$, second 2000$ and the third 10.000$. You easily rack that amount of money when playing Terror is Reality at the start of the game.

*Save Denyce, kill the looters. Bring Denyce to the Safe Room, talk to Sulivan who will give you the key to the maintenance rooms. But: Time to safe your first "real" survivors. They are there once you walk through the doors. Bring them to safety (you cannot do anything wrong as they are near the Safe Room and the AI of survivors is better than the first game!). In later playthroughs talking to Sulivan is not needed as the maintenance key gets in your inventory by default.

*After the first two survivors are in and you got the PP for both, restart the story. It allows you to keep the level and PP you already got. Press so you skip Terror is Reality and the escape from the arena with Katey. You end up in the Safe House. Rinse and repeat from here to level 25. Not hitting results in the intro being played and do Terror is Reality all over again, and escaping the arena. Which only costs time.

*At level 25: Start a "serious" playthrough. Save every survivor, kill every psychopath, do all the cases, get Overtime mode. It will get you AT LEAST in the zone of level 50. (I ended at level 48 when I went for the last boss before Overtime Mode)
You easily get to level 50 while being in Overtime Mode, and go for an achievement like "having a gas" which is killing 1000 special zombies with the "chopper bike" motor plus chainsaw for 20 PP per kill, 500PP per 100 kills and 20.000PP per 1000 kills.

It looks like a lot of stuff to do for the first 25 levels, but once you get the route and the hang of it, it is the fastest way to quickly earn level 25.
It took me about 90 minutes or so to do. When you do a seperate little playthrough for the keys to the sports car (500.000$ instead of 2 million in OTR) you can even speed up getting Denyce to the Safe Room and such.

If you give a negative thumb, tell me why and I will add it to the solution.