I own Omnisphere and find it to be incredible musical and flexible. And you could literally spend eternity experiencing every single patch available. My biggest gripe with it is that you cannot upload your own sounds (unlike Kontakt, Alchemy, and other sampler/synths). I happen to love the granular effects you can get in Omnisphere and I wish so often that I could import my own samples.
I discovered Camel Audio's alchemy. It's a different beast, but not that different, and it allows you to upload up to four wav files per plugin instance. It also comes with a large library (but nowhere near the 40GB of material in Omnisphere). It definitely depends on your needs and workflow, but always something to keep in mind. Also, as a student you are eligible to buy Alchemy for $125 through Camel Audio's academic pricing.
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Just make sure you stick to music and not sound design. Omnisphere can't legally be used for sound design. I remembering reading some big blog post about it but can't find it.
Omnisphere is AWESOME!! It gives you control over your patches you wont get elsewhere I dont think. Great presets, but really great customizable features. You can even go into their source sound files and build from scratch and synthesize all in one. Offers dynamic playability to real-world infused synthetic sound and vice versa. Native Instrument synths are cool and can get a lot of different sounds, but they dont sound quite like Omnisphere. Its a very musical plugin.
Either that or NI Komplete are pretty widely used, because they're probably the biggest single "sound banks" around. I've heard people call Omnisphere a standard tool in DAW-based film scoring (which I'm not sure if it's a good or a bad thing, even though the patches are made by very experienced people and thus sound extremely good). Alchemy is the closest contender and it's a better synth, although the patch content is a matter of taste (Omnisphere likely still has more and "better" overall content as it has a lot of legacy samples in it that have been in products that the Omnisphere team has worked before).
But, if you have a sampler e.g. Kontakt that has loads of good banks made for it, then you may equally well purchase just sound banks for your sampler.
NI Komplete is powerful, Iris is wonderful, but Omnisphere so often gets the job done. If I was stuck on an island and hired to compose "a video game cinematic trailer" I would pack Omnisphere while shedding a tear or two for Kontakt and Reaktor.