I, too, loved this movie. I still think IG is QT's magnum opus, but this is really great too. Much more in line thematically and visually with his early work, but showing maturity and restraint.
Performances are great. How much Pitt has aged to look like Robert Redford is uncanny, and cool. I'd totally watch a Butch and Sundance remake with him in the Redford role. DiCaprio is unbelievably good here as well. It may be his best performance ever, and he's had a lot of good ones.
RE: Manson... I may have been burdened by my deep knowledge of Manson lore here. I went in telling myself to shut off that side of my brain. I had heard rumors of an IG style history rewrite at the end. In the context of what QT was saying about the death of old Hollywood (in his fantasy of it never dying), the alternate history made sense. Though I'll go the other way here and say I found it more off-putting than his torching Hitler in IG. Maybe it was the intimate gruesome violence of it all. I do like that the Manson stuff was just sort of peripheral to the Rick Dalton / Cliff Booth story.
And make no mistake OUATIH is a fairy tale romanticized version of that era of Hollywood. Yes, the Manson murders brought in paranoia, but the seedy underbelly had been there since the inception of the studio system. Hollywood has been a corrupt criminal enterprise from the beginning; California was still basically it's own fiefdom when the studios were founded. The owners of them were people who thought they were above the law and could do what they want with whom they want. If Sharon Tate hadn't have been murdered by Manson (rumored to be Hollywood's pimp du jour before he wen off the deep end) something else would have happened eventually.
But I'm sort of cynical about that whole era after spending so much time in the Manson gutters.
OUATIH is a feel good movie, maybe the only QT movie that truly does lave you feeling warm.