I used RealFlight to train for about a month before I got my trainer going. I found it to be highly realistic. What I did on the sim I could exactly duplicate out at the field. I think some planes definitely fly more realistically than others. That might be why people have divergent opinions. For example the Fokker Triplane in the expansion pack lumbers along at a speed that absolutely defines gravity. Other planes, for example, the "Fandango" electric flyer are so quirky I can bearly keep it them in the air -- but then that's great practice too.

In the end, I feel that RealFlight was well worth the money and not something I'll stop using now that I've solo'd. It's great practice to take a quirky plane with dangerous tip stall characteristics and put it into a spin and then try to recover. It's fun practicing left thumb only flying (rudder and throttle) before trying it out on the real plane. Later when I get better I can imagine myself working through whole routines on RF before the real deal.

Can you learn without a good sim (or any sim at all)? Of course, but don't expect it to be any cheaper!