my routine currently looks like:
I do rack pulls as my last movement on my back day, instead staring with rows and pull downs/chins.
chest day is centered around incline BB, DB floor press, and machine presses (no flies, DC stretch at the end)
arms are trained in 6-8 rep range.
shoulder day's primary focus is DB laterals and rear delts, pressing comes last (a la John Meadows)
I do separate legs, because they are an enormous muscle group.. do you expect to be able to train your glutes (largest muscle in your body) along with your quads (another massive muscle), and your hamstrings (another massive muscle), effectively all in one workout?
by the time im done with squats and leg press, im running on fumes.. so hamstrings get neglected. In the same way, if I start with hamstrings, my squatting strength suffers.
just some thoughts