I know almost all free VSTIs and Atlantis is one of the best and incredibly unknown to most people. Even if at first looks complex it actually isn't and the modulation possibilities, waveform morphing and so on are now the awesome features in Serum. I have checked also the quality of the signal it produces with an ocilloscope and it is very good as far as I can tell.
The filter is a story in itself and it is very useful also standalone, with other instruments.
You can import waveforms like the AKWF's (wave format), putting them in chips folder in your user's Atlantis folder. You just shouldn't use too many, it seems. I hvae selected some from the AKWF collection that are the most useful. If you have Serum you can use its waveforms too, by cutting single cycles from their wavetable in wav format. It has up to 256 cycles stored in one wav. You can do virtually anything from there on. But the morphing is obviously not the same, it morphs just between two waveforms and not across the whole wavetable as does Serum.
I have studied Atlantis quite well, and can answer some questions, too.
Oops, I lost all the presets for Atlantis, There's a lot of presets done by randomize parametrers, but Atlantis is a synth that needs an initial effort to understand how its envelopes and modulation work. Randomness doesn't work to get all the power of this waveshaping synth. In fact, it's hard to get hard tones or low basses. This one is great for pads. I'll try to upload some of mine.