Given how important it is to make Aiden O'Malley's kidnapping look like a "jailbreak" (so that the cops won't immediately suspect Derrick) - why is it that neither Niko nor Packie take greater pains to actually try and hide the body?
On a similar topic, one "random character" mission involves you having to deposit a car with a dead body in it in the river. At one point I thought I'd be clever and blow the car up. I failed the mission, getting a statement like "the car is trashed, now the cops will find the body!" Even though what was left of the body was burned beyond recognition along with the rest of the car!
It's called dental records. Easily recovered from a burnt body, not so much from a body no one can find because it's at the bottom of the ocean.
The whole point of sinking a body is to make sure it isn't found for at least some time. With every day the trail gets colder and colder as the perps get more time to cover up their work, forensic evidence degrades, possible witnesses forget crucial things and paper work gets buried. If visiting the icmp has taught me something then it is that you can identify pretty much any body as long as there is something left.
Back to Aiden, according to the in-game news, his body was found washed up on shore shortly after he dies. Isn't this supposed to be a massive problem? Why don't we hear about it again?
It would be a problem only if they could actually get anything useful from the body. As far as they know, the guy was broken out of jail, then found with a bullet in his head on the beach. They know that he was murdered and dumped in the sea, and that's about it. There's no murder weapon to connect any bullet left in the wound to, nobody ID'd the two perps who broke Aiden out, and it's probably been long enough that the witnesses don't remember enough details to be useful. It's a cold trail.
The point of killing him that way is that the McReary's are the only ones with any motive to kill O'Malley. Even without physical evidence, that's enough reason for FIB to get up in the McReary's shit.
It's just another example of the GTA IV games' overall theme: Almost everything the PCs do is basically futile. Most of your employers end up dead or in prison. The people closest to you die. Whatever you're struggling to keep together falls apart in the end. Niko, Luis, and Johnny are ultimately losers who can't get anything right.
How come Niko gets to keep Michelle's car after their first date?
Gameplay and Story Segregation. If you wanted an in universe explanation, she has no actual connection to the car, being a government agent, and could probably just get a new one delivered. It would also make Niko easier to track if he kept the car for himself, since they now knew what to look for on the roads.
After shooting a bunch of cops and escaping from a huge raid in Snow Storm, why does Niko just hand Michelle the cocaine he retrieved?
She said "please".
She did mention she was an undercover agent for an undisclosed government agency at that point, so that probably comes with the implication that she could have Niko and Jacob killed on the spot if they refused.
Why is it that only Little Jacob and (possibly) Roman help you in the final mission? What about Packie, Dwayne, Brucie? Especially Brucie, wouldn't it have made more sense for him to bring you his helicopter instead of Little Jacob hijacking an Annihilator?
Packie's probably too busy looking after his grieving mother, who had already had one son killed and another arrested - and that's before Kate's death in the Revenge path. Dwayne may have taken back control of his old gang with Niko's help, but he's trying to keep a low profile to keep from being thrown back in prison, and is also likely still working out his depression issues. And while Brucie might act tough, would you really want him backing you up in a fight?
No, but I wouldn't exactly want Roman either.
Speaking of which, where did Jacob get an Annihilator?
He used a cheat code on his phone.
When you call (or get a call from) Packie on the "Revenge" path, he is indeed looking after his mother, and he's not in such good shape himself after Kate's death (I got a call from him right after finishing the last mission).
What is with the hate for Michelle?
Niko's Berserk Button is getting betrayed by others, and most players probably can't help but empathize with him after awhile.
Niko can earn a safehouse in North Algonquin if he decides to kill Playboy X for Dwayne Forge. Later, in Ballad, it is revealed that Luis Lopez owns an apartment just one block south of Niko's safehouse. Given these men's proclivities and previous interactions, why was the possibility that they may stumble upon each other right outside their respective homes ignored?
Ignored by whom? None of the characters in the game know where both men live (the word "safehouse" is relevant here) so there's no one to raise that possibility. As for the developers, they may not have completely fleshed out Luis' story at the time they introduced him in the main game. Since they can't add a scene with Niko into Ballad without having had at least a similar encounter in IV, they basically had to conclude that canonically they just never met on the street. Further, as you noted this scenario only presents itself if you kill Playboy, so another option is that the canonical path is killing Dwayne. Which would neatly answer this question as now Niko can't hang around Playboy's neighborhood any more.
They're only in the same place three times, and only interact face-to-face once (IIRC). So even if they did pass on the sidewalk, they wouldn't necessarily recognize each other.
What is with the girlfriends? I take Michelle out on a date and she tells me to get a car. She watches me smash the window out of a nearby car and hotwire it and isn't bothered in the slightest. Then a few minutes later I shoot my pistol once and it doesn't hit anyone, next thing you know: "Michelle is scared" and the date ends. On another date she literally helps me carjack someone, but I get into one fist fight and she gets scared and ends the date like last time. This isn't irritating, matter of fact it is hilarious, but why the selective fear?
Probably for game play reasons.
Johnny: "I wouldn't want this Niko Bellic after me. Guy is deranged." Is "Bellic" such a common name in Liberty City that Johnny doesn't connect Niko with that Roman Bellic guy he just kidnapped?
By that point Johnny's probably long since forgotten Roman's name, but even if he did make the connection he would probably figure if Niko was ever going to come after him he would've done so already; for all he knows, Roman's dead, and Niko's had plenty of time to seek revenge.
Where does the diamond money end up? The diamonds themselves are found in the trash by a homeless vet. Is the cash just collecting dust wherever Jim hid it before he died?
I was under the impression the cash was retrieved at some point or another by Johnny; in one of the post-game phone calls he mentions wanting to send some of it to Jim's wife and kid, IIRC.
Why do characters have the ability to put on a motorcycle helmet after getting on a motorcycle, but don't have the ability to put on their seat belt after getting into a car?
Seat belts don't appear to exist at all in the GTA universe up until GTA V, unlike helmets which can be seen being worn by various NPCs throughout the series.
Why are there news reports about the serial killer operating in the city, who's suspected to have killed a few people, but nobody makes the connection between the rash of crimes involving Niko, who murders at least 50 people during the game, and can potentially kill hundreds more if the player chooses to?
Rampages that player chooses to go on are not canonically part of the game. Only the ones required for missions, and all those deaths are crime based. Not the MO of a serial killer.
The news does consistently make a connection to the majority of the more serious crimes Niko commits, only to terrorists instead of Niko.
In Three Leaf Clover, NOOSE uses Police Stockade inmate transports to bring tactical teams to the bank. Why use an inmate transport to transport combat teams when NOOSE has Enforcers (Armored vans used to transport teams at high wanted levels that are very similar to the Police Stockade) available?
Why is it that you automatically get six stars even if you sneak across the closed bridges through the subway tunnels? There's no way the police can see you.