It's always a balancing act when reviewing documentaries. How to judge it mostly on its cinematic terms without letting personal opinions on the subject matter have too much influence? Making a documentary is a lot more unpredictable than a fiction film, where practically every story decision is conscious. As far as edition, direction, camera-work and all other artistic aspects can go to present a story, it's still only SO far. It's not rare for a documentary's story to go in all sorts of unexpected directions thanks to the people, subjects and/or events depicted.
As a documentary focused on a specific place (Milan's Reffetorio Ambrosiano soup kitchen) during a specific time (Expo Milan 2015), "Theater of Life" would seem to have a limited focus, useful to prevent the film from becoming too dispersed. The subject being food waste, which is personally one of my biggest pet peeves, would've apparently made me judge it favorably as I agree with most of the opinions on the matter shown on the film. However, despite the focus being so limited and the subject so personal, the film unexpectedly ends up following a few too many threads and boarding a few too many subjects to be an in-depth portrayal of any of them.
Then again, it never really seems to want to be that. This is a humanist documentary, about human emotions (Bottura's ambition not to see leftover Expo ingredients go to waste like so much food around the world does on a daily basis, the diners' different desires, including the ultimately humanistic one of not wanting to be judged by one's conditions and habits but for WHO THEY ARE) from all sorts of humans (top chefs like Bottura and René Redzepi, refugee, migrant and Italian diners, religious and charity workers involved in the Reffetorio). Its humanist agenda might ultimately make the film feel like a somewhat superficial look of it subjects and not as engrossing as it could've been but it still seems to be the filmmakers' actual target.
Much like most of the chefs' ideals, which come off as a bit naive and idealistic when contrasted with the diners' not hopeless but more realistic and jaded ones, "Theater of Life" might seem that way in comparison to far more in-depth and objective food and food waste documentaries. It is still an emotional look into the lives of the "less fortunate ones" and with this focus, it might actually end up being more effective in portraying the absurdity of the current worldwide food waste and homelessness crises than other "drier" ones. There's also a balancing act in documentaries between emotion and objectivity, specially in terms of which works best for a specific purpose. While I might not have fully agreed with this film's balance, I can still understand and respect it.