His “masterpiece” or not? Help me decide, won’t you? I have this film on tape and every time I see it, I think: “I would follow this man anywhere!”
There is one other film where he appears as a ghost and one keeps hearing his footsteps throughout, but I cannot think of the name, and I am sure it hasn’t been released on either VHS or DVD, but Lee Marvin sure had some stones hangin’ down, didn’t he? 
Quasi
PS: “All The Beatles love ya’!”
The Big Red One is considered director Sam Fuller’s film with the most mainstream acceptance and acclaim as well as his homage to all the men he knew in the military and those who never made it back home. I like Lee Marvin’s acting in the film, but I wouldn’t call it the pinacle of his acting career. I know it was a very personal film for him, and it shows during the movie, since he was a Marine in the Pacific theater of WWII and was severely wounded during the bloody fighting on Saipan.
For his acting, I would rank his roles in films like Monte Walsh, Cat Ballou, The Emperor Of The North, Hell In The Pacific, and maybe Pocket Money (a personal favorite of mine, I consider it an underrated gem of a film) ahead of the Sergeant in The Big Red One. It is very similar to other tough guy roles he had done over the years, that’s why he was perfect for the role.
I believe you mean the John Boorman directed crime drama/ghost story Point Blank from 1967. One of my all time favorites of Marvin’s film career. It was on VHS at one time, I’ve seen copies at various video rental stores, but I taped it from AMC before they added commercial breaks and screwed up their programming.
I would also add in The Dirty Dozen and The Man Who Shot Liberty Valence, though I did like Big Red One a lot.
OK, I’m going to throw in a few of my favorites. Personally, I never liked Big Red One. I always felt that Marvin was just “mailing in” his performance. He just seemed to stomp through it. Much like he did in the later Delta Force. OK, maybe not that bad.
In many of his (what I consider his really good) movies he added something more. Like in The Man Who Shot Liberty Valence, there was that homicidal streak that just dominated the screen (and when you consider Jimmy Stewart and John Wayne were in most of the scenes he was in - that took some doing). You believed he was capable of true, sadistic murder.
You saw the power and that “something” in the Wild One too. What other actor could take the screen away from Brando? Yet Marvin did it. The only one that I ever can remember managing to do it.
A total departure for Marvin was the wonderful Ship of Fools. An ensemble drama that called for Marvin to do a non-action role. He stepped up and did a great job. I think he was nominated for an oscar for that one.
Two of his three excellent westerns have already been mentioned. His comedic turn (up to then unknown - it should be mentioned - OK, OK there was Donovan’s Reef) in Cat Ballou was delightful. The personal, very real cowboy in Monte Walsh. Compare his version and the recent Tom Selleck version. It’s like comparing apples and rocks.
The final of the weatern trio is The Professionals. In that film he appears with academy award winners (or soon to be winniers) Burt Lancaster, Jack Palance, and Robert Ryan and yet it is his film by his underplaying of the part. Quite impressive.
I also loved Point Blank that confused aspect he added to the part of the killer was wonderful. You saw something of that in The Killers too. Another very good film of his that I have heard was loosely the basis for the later Point Blank.
I will give you that Big Red One is a solid performance, but hardly his “masterpiece”.
TV
I liked the Big Red One okay, but as far as Lee Marvin performances go, I prefer…
The Dirty Dozen
The Killers
Bad Day at Black Rock
and
The Iceman Cometh