It's a powerful synth and sampler rolled into one! You might think this makes it not as good synth, or not as good a sampler, but it really holds its own against the top of the line in both respects. The engine has a really good sound. I'd say it has a clean, tight, focused sound, but can get dirty if you want it to. The sound pallet, as you might expect, is extremely broad, and the modulation options make it potentially very expressive.
Love how you can stack as many filters and as you want! You aren't limited at 1 or 2 like many synths are. It's great how you can use many of the effects as filters on a per voice basis, and stack them. Especially love the variety of Xpander filters, with the overdrive options.
The modulation options are fabulously endless! The number of envelopes and filters is not limited like it is on many synths. Only thing lacking in this department would be the ability to use one of the oscillators as a modulator.
The scripting capability might fall under this category, and I don't know of any other synths that offer scripting capability. For samplers, Kontakt does, but there are no built in synth oscillators like there are in Falcon. By the way, if you're into acoustic instruments you can get some really impressive samples from AcousticSamples.net which are all compatible with Falcon.
The fact that there are 15 different oscillator types is great! The wavetables are top notch, and the ability to generate wavetables based on images is very nice! The various phase distortion algorithms are very good, though there not quite as many as Serum (but then Serum is missing a LOT of the functionality that Falcon has). By the way, I hear you can import wavetables from other synths, such as Serum.
Unison is very good, and can be done on an oscillator level (up to 8), and on a layer level (up to 256, and multiply that by 8, and you've got a lot of oscillators!). The fact that you can stay as many layers of different types of oscillators to combine synthesis types gives this synth synth a potentially huge sound.
I used to wish there was a way to modulate one oscillator with another, for FM or AM (it has an FM oscillator, but that can't modulate or be modulated by other oscillator types), but now with 1.5 they have added FM capability in the Wavetable oscillator! Excellent update. Only thing I wish about this now is that it had the capability to choose the type of oscillator it's being modulated with. It seems it currently always uses a sine wave.
The pluck oscillator is rather unique, and can make some interesting sounds. Among other things it can use samples as an impulse.
All the various granular oscillators are quite nice! Some of them can get quite CPU intensive at times, but some of them are very high quality! The Stretch oscillator reminds me of the graintable synthesis of Malstrom (which I quite like), in that you can scan back and forth across the wave and change it's speed, but it's even higher quality (and more CPU) and you can do it with your own samples.
The effects are great! Especially love the lush reverb. It's especially powerful to be able to stack as many as you want, and control them via modulation sources.
The patches for this give a nice demonstration of what it can do, but there could be more of them, and there is lots more to be explored. It's good that there are UVI libraries available for sample material. It seems to be compatible with all the 3rd party UVI libraries too. I'm sure sound designers will be releasing lots of patches for this synth in the future, because it has massive potential.
The sampler capability is probably on par with Kontakt, and even has scripting like Kontakt does (though the language is different), but Kontakt doesn't have the synth options that Falcon does, and thus probably why I hear Kontakt is a little more efficient on the CPU. You might compare it to Omnisphere, though the Falcon library is not quite as big but it has more synth options, and I'd say a better UI that allows you to see more things at once. You might compare the Wavetable capabilities of Falcon with Serum, and I think the quality is about on par with Serum. I think it most compares with MOTU MachFive (in fact I think under the hood it seems basically like an upgraded version of the MachFive engine), but has more oscillator, effects types, and some other things, and doesn't import as many sampler patch types.
Overall it's a very deep instrument. I don't think there is another synth that combines as many different synthesis types, and does it as well! The sheer breadth of the sound palate makes it a workstation you might never have to leave. Great for sound designers! I plan on making some patch sets for this, and releasing them in the future.