I came across a really good scientific report that confirmed what we have assumed: GENERALLY, the higher the nicotine, the greater the hit. Nicotine hits the top of the airway passages and causes the muscles there to contract sharply. It's like gasping, or being punched in the chest. If the hit is strong enough, a user involuntarily coughs to expand the muscles.
But .. and this is interesting .. the PH of the liquid has an effect also. Alkaline cigar smoke, if inhaled, has a much harsher hit than acidic cigarette smoke, even when the cigar smoke has less nicotine. That means a liquid maker, to increase hit without relying on nicotine, might manipulate the PH of the liquid so that it mimics a nic hit.
Generally, the history of smoking has been an attempt to mitigate the hit, to create smoothness instead of harshness (that's where menthol with its analgesic effect comes in!). What e-smokers seem to be asking is that the smoothness-harshness level be set at that of popular tobacco cigarettes. Surely the liquid makers can do that with some experimentation.