I'm not really sure how much more "depth" one could expect to see in this film. It's a day in the life of this severely depressed gay man who is planning to kill himself. What more depth does the story need? It seems to me that its the story itself (or the way Ford handles the story) which people have problems with.
Two more quick thoughts.
*SPOILER* First, apparently in the novel, George doesn't die at the end of a heart attack. So I'm really dumbfounded why the screenwriters decided to alter the ending in this way. It almost seems like the writers are giving the audience the finger: "This guy has been through this much, he's finally decided not to kill himself, BUT WAIT... HEART ATTACK!" What's the point?
Second, for a movie which centers on a man's loss of his lover, we don't learn much about George's history with Jim. As a result, I never really felt George's pain. I understand he's depressed. I understand life has no meaning for him anymore. But I never really felt it. Why is he so upset? I don't mourn the loss of Jim, so why should George? I think this is probably the primary flaw with the film.
Third, the young student never really felt developed for me. I wasn't even sure if he was gay by the end of the film, though it was certainly suggested. I also don't see why this young boy produced such a change in George. He has the big epiphany toward the end, but it sort of seems like a plot device rather than something which flows from George's character development.
Anyway, after thinking it over, I think I probably enjoyed the first half of this movie the most, but toward the end it seemed sort of strained to me. The ending also didn't work for me - and endings are usually the most important parts of a film for me.
As for how color is handled in the film, I enjoyed it. George sees barely any meaning to life, which is why he plans to kill himself. Yet, he still sees glimpses of beauty to existence - and when George sees it, we see it. This worked great at first, but upon thought, it sort of seems like a gimmick. Why is this technique not used to full effect at the end when George finally has the epiphany that he wants to live?