Dan Owen’s review published on Letterboxd :
Well... a lot of the surprises were spoiled by the trailer, as to how strange the premise of Swiss Army Man is, and how far it takes things. If you don't already know, it's about a suicidal cast away (Paul Dano) who seizes a chance to get back to civilisation after discovering a washed-up corpse (Daniel Radcliffe), that has a variety of bodily functions that prove useful in surviving and escaping his island.
I appreciated how deep this movie tried to get, quickly evolving beyond that ridiculous setup. It delves into real complexities of human relationships and how it's difficult to connect deeply with people beyond social politeness. And it's beautifully directed at times by "Daniels", with some smart visuals and beautiful compositions.
Swiss Army Man was fairly enjoyable and refreshingly different to anything else you're going to see, for the most part, but I never totally lost the feeling this was a self-parody of independent low-budget comedies entered at the Sundance Film Festival. But while the trailer felt like a clever joke, the actual movie does have a lot more substance than you might be expecting. Just don't expect a lot of it to make sense, in terms of rational human behaviour and anatomical logic.