I have to disagree with you on Dead Rising 3. They completely fucked up by trying to make it all serious that it lost what made the older games good in the first place. Dead Rising 4 tried to correct this but fucked up by being way too fucking linear. DR2 is always going to be the best in the series unless the remakes end up being spectacular. I'm not holding my breath on that happening.
I disagree about the tonal issue, it fits with the game being more grimey and realistic. Don't forget, this was supposed to be the grand finale of the trilogy, and if you played Case West, you would know that shit has gotten dark once PhenoTrans' dirty laundry got exposed. This was to be expected, especially since the events of the game see more dead than possibly any other outbreak in the franchise.
The game still let you do funny stuff, but the game definitely had an air of an endgame hanging about. It gets worse when you play the DLC and see just how fucked the situation is for other characters(the biker one was pretty lighthearted, tho).
The biggest improvement DR3 had, and the reason why I like it so much, was how much smoother the gameplay was. Good lord did it feel great to just ride around the town and collect things or kill zombies, you could do all that in earlier games but it's so much better here. Everything is smoother and better, fighting, movement, vehicles that are now integral to moving around, platforming, combo weapons, even friendly AI is much better and they escort you rather than the other way around. Really, the biggest flaw of the game is that it was too short and easy, I genuinely think the "nightmare mode" was the original normal difficulty, before the game was dumbed down so it could be more palatable as an Xbox Day One title.
Then Dead Rising 4 shat up everything by...well, TehSnakerer made a video that's 2 hours long covering this game, you can give it a watch if you want to know how truly fucking awful that product is(and there is a video that also goes in detail what went on behind the scenes by "DidYouKnowGaming". The game was originally going to be a reboot and resemble Last of Us of all things, until Capcom pulled the plug and forced them to make another Dead Rising in the last minute. Ever wonder why DR4 has a fucking sneaking mode?)
Edit: The DYKG video
It just occurred to me that while limited, Dead Rising 3 also has mods for it. Is it one of the effected games?