Usually I'm not a fan of multi timbral VST's. You can create whole soundscapes from a short field recording or a sample from a record. You can however import your samples and use them for granular synthesis and that I really love. I'm fine with that as I never use my own samples to create realistic instruments anyway. Omnisphere is not a sampler, meaning you can't use your own samples and create complicated keymaps, switches or round robin setups. I'd don't think I'd buy these effects to mix with, but as a complement to the sound engine I think they're fine. A big bunch of effects really put the icing on the cake.

All go through a subtractive synthesis engine that allows you to sculpt the sound to your liking. There's an extremely large amount of sampled 'soundsources' available plus a very decent amount of modeled analog waveforms.