I think Reaktor, as a softsynth, provides unparalleled synthesis power and capabilities. It's ability for you to go into the the different modules, alter their function, then set up your own unique routing system from Oscillator, Filter, Amp, FX whatever you want is outstanding. It has wavetable synthesis, additive, subtractive, and FM synthesis.
Furthermore, it has an array of softsamplers, and different modules which give you the craziest FX and power to manipulate samples and beats known to man.
Some may say that Reaktor is guilty of "cutting corners" regarding its necessity of using a CPU as its powercore (this is true of ALL softsynths), but the power it gives you is something that could not have been dreamed of a couple years ago. It indeed is the total package.
Granular synthesis, which is ANOTHER form of synthesis I forgot to mention is another way to make great and unique sounds. I literally sit in front of it for hours, routing modules to try to make interesting sounds.
A similar synth with very very powerful synthesis capabilities via a software control program is the Nord Modular (but it's not a softsynth, it runs off DSP.) That is great and a friend of mine has it. It's incredible.
You said you want something simple, and Reaktor offers you simple "analogue synths" with a few knobs and controllers. I suggest you not get ripped off by buying a softsynth that emulates only one synth, but get something like Reaktor, where you have more softsynths at your disposal as you develop and understand synthprogramming further.