Okay, so obviously I can't fit in all my thoughts on The Godfather and its awesome sequel (Part II, that is, I have no interest in seeing Part III).
Anyway, if you haven't seen the movies, read no further. Instead, go watch the movies.
If there's a murder that shows Michael Corleone is officially evil, it's not Carlo's.
I'm not saying murder is ever a good thing, but Carlo is really a terrible, terrible person. Not only does he beat his wife Connie and cheat on her, he also gets one of his girlfriends to call Connie so that Connie is angry about him cheating on her so that he has a trigger to beat her so that he can set up the murder of Connie's brother Santino ("Sonny"). A bad guy. I mean, sure Sonny beat up Carlo after hearing about how Carlo beats Connie, but Sonny was the guy who introduced Carlo to Connie in the first place. In the end of the movie, Michael tells Carlo he's not getting killed, and then Clemenza knocks him off. So yes, the murder does show how Michael is cold-blooded. But it's hard to feel too bad for Carlo.
Tessio, Fredo, and Family Murders
In The Godfather, Michael has Sal Tessio, one of his father's caporegime, knocked off, which seems fair. Tessio plotted to murder Michael. What amazes me about this exchange is how neither Tessio nor Michael seem remotely mad at each other. Michael doesn't seem to feel betrayed by Tessio, saying "It's the smart move. Tessio was always smarter [than Clemenza, who is loyal.]" Tessio says "Tell Mike it was nothing personal. I always liked him." There's not much emotion on the part of either. Tessio, though a minor character, is in that sense more like Michael than perhaps any other character in the movie. Both characters seem to respect each other as "businessmen."
Similarly, while Tessio plots to have his best friend Vito's favorite son (Michael) killed, Michael watches from shore as his own brother Fredo is shot while fishing. Now Fredo was part of a plot to have Michael killed, but Fredo didn't really know that the information is being provided to have his brother killed. Fredo's just essentially a helpless guy in way over his head. His mistake was that he didn't know his place, thinking he could get involved without getting manipulated. He should have known better. As Michael says in the original, "Fredo, you're my older brother, and I love you. But don't ever take sides with anyone against the Family again. Ever." So, Fredo really was just an idiot.
Is this a crime that deserves death as a punishment? I vote no. Not when it's your own family. But by the end of Part II, Michael is pretty numb about the notion of family. It's not hard to see why: his sister's husband helped plot his brother's murder, his dad's friend and capo helped plot an attempted murder of him, bullets fly into his bedroom while he's there with his wife, his brother aided in an attempted murder on him, another capo (Frank Pantangeli) who lives in the house where Michael grew up has been brought in as a witness to testify against him, both of his parents are dead, and his wife aborted his son saying she didn't want to bring someone like him in to the world and then left him. While it doesn't effect his mental sharpness, all of this crushes Michael's humanity.
No Hope at Escaping the Mafia
This is, perhaps, the most upsetting message of the movie. After all, if there's anyone who could have escaped the mafia life, it was Michael. Vito tells Michael that he knew Santino and Fredo would have to be involved. Santino was hotheaded and clearly excited about mafia life, and Fredo just wasn't really smart enough. Tom Hagen, though he's not a "wartime consigliere", is also pretty tied to the Corleone family as he was rescued by them from a bad family situation.
But Michael is a Dartmouth grad and a war hero with a girlfriend (later his wife, later his ex-wife) Kay Adams from outside the mafia world. Vito doesn't want Michael involved in the mafia, and Michael doesn't want to be involved either. But when an attempt is made on Vito, Michael decides to help the family and it all goes downhill from there even though Michael always wants the Corleone family to be legitimate.
I really like Michael, so I find the two movies very depressing. I guess if you just want to watch it from a superficial level you could appreciate it for following the action, but I don't think the movies ever let you do it. They give the characters too much depth, make them too human and too recognizable, for you to distance yourself from the way the characters, especially Michael and in Part II Vito, grow and change.