Erik,
A cropped 28 on an M8 and a 35mm on FF have approximately teh same angle or field of view. This means that the positioning of the photographer remains the same to capture the same stuff in the frame. This means that the relationship in size between near and far objects also remains the same. This means the look also remains the same apart from one thing. F4 for example gives more percieved depth of field on a 28mm compared to a 35mm on FF as DOF is a function of focal length. This is the reason why an 80mm f4 lens shot wide open on a Mamiya 7 prodes the same background blur approx as a 40mm at f2 on FF. The shots will look almost identical in terms of persepctive etc but because the Mamiya has double the focal length (to get the same FOV as the neg is twice as long) it would produce a more diffuse background at the same f number. BUT if you double focal length you need to stop down two more stops to get the same depth of field.
Soooo, what this should mean is that if you shoot a 28mm on a M8 and a 35mm on FF and use the appropriate F numbers to get the same DOF, the two will to all intents and pursposes be identical. Just like my 90mm on 5x4 behaves just like a 28 on FF in terms of persepctive etc, only I need to shoot at a much smaller aperture to get front to back sharpness in landscapes compared to a 28mm on FF. On 35mm for a landscape I might shoot at F8/11, but on 5x4 more likely F22/f32 for teh same scene (unless I can use movements).
It realy helps to mess around with different film formats to get a feel for this. I shoot 5x4 and 10x8 too. My 150mm on 10x8 produces an identical look to a 75 on 5x4, only I need to stop it down more to get everything sharp. Many people discount the Mamiya 7 due to the slow 80mm f4 lens and then gaily use their 35mm cron thinking they can isolate their subject more. They cant. They are probably getting LESS isolation. My 90mm is a moderate wide on 5x4 but seriously wide on 5x7 and gives that stretched out look just the same as a shrter FL would on 5x4 (such as a 65). For teh same reasons the Mamiya 7 150 4.5 equivalent FL on FF would be about 75mm. However, you get FAR less DOF at f4.5 on the mamiya lens than you do on a 75 lens on a 35mm camera. About two stops less. This is the argument used by advocates of smaller formats, who say as you need to stop down less on smaller formats (shorter FLs for the same framing give more DOF) you can use slower film thus removing the disadvantage of reduced real estate.
I am not technically minded so if this contains inaccuracies, please correct me! Hope I am not leading people astray here :O