Axe-Fx Ultra is completely brilliant. The user interface is really intuitive but gives you a truly insane amount of options.
This is basically how it works...
The input signal gets routed to a 12x4 grid. So you can have up to 12 effects in series and up to 4 parallel chains. You connect each chain to the output block and its 4-way mixer/panner.
You can connect the output of any block to the input of any other block and can split outputs up to 4 ways. The Axe gives you 2 insert parallel mixers so you can mix signals before the input of any block.
To modulate parameters in the blocks, you have access to 2 LFO's, an envelope follower, pitch detector, 16-step sequencer, 2 ASDR's, and 8 external controls (can be expression pedals, MIDI CC's, etc.) You can use any of these modulators as many times as you wish on as many blocks as you wish.
The Axe-Fx Ultra has a really comprehensive assortment of blocks to choose from.
Amp Simulator
Cabinet simulator
Chorus
Compressor
Crossover
Delay
Drive
Effects loop/aux out
Feedback send/return
Filter
Flanger
Formant filter
Gate/expander
Graphic equalizer (x4)
Looper
MegaTap delay
Mixer
Multi-delay
Multiband compressor
Noise gate
Pan/tremolo
Parametric equalizer (x4)
Phaser
Pitch shifter
Quad chorus
Resonator (four resonant comb filters in parallel)
Reverb
Ring modulator
Rotary cabinet
Stereo enhancer
Synth (2x dual-voiced monophonic synths)
Vocoder
Volume/pan
Wah-wah
You basically get 2 of everything and I have to say, pretty much everything sounds excellent. I'm definitely not missing my Eventide effects.
The synth possibilities are incredible. These are the parameters for the synth block (from the manual):
TYPE - Selects the type of waveform. Sine and triangle are the smoothest while the square and ramp types are more buzzy. Available types are: sine, square, triangle, sawtooth up, sawtooth down, random, pink noise and white noise.
TRACK - Selects the type of input tracking. OFF allows the frequency and level to be set manually via the FREQ and LEVEL controls. ENV ONLY selects the level to be controlled by the envelope of the input with the frequency set manually. PITCH+ENV selects the frequency and level to be controlled by the pitch and envelope of the input.
FREQ - If input tracking is set to OFF or ENV ONLY this paramter sets the oscillator frequency.
SHIFT - Shifts the frequency of the oscillator up or down in semitone steps. The oscillator can be shifted +/- 24 semitones.
TUNE - Detunes the oscillator slightly. The oscillator can be detuned +/- 50 cents.
DUTY - When using the TRIANGLE or SQUARE waveforms this parameter controls the duty cycle of the waveform.
LEVEL - Controls the output level of the oscillator.
PAN - Controls the panning of the oscillator.
FILTER - Sets the cutoff frequency of a low-pass filter after the oscillator.
Q - Sets the Q of the post-oscillator filter.
ATTACK - Sets the attack time of the envelope follower on the input.
You can modulate anything with the modifiers I described. So far, I've gotten a lot of awesome results stacking the two synths in parallel (4 oscillators!).
I'll tune one of them lower and set the oscillators down an octave. I'll use the 2nd synth to get higher frequencies and high-mid frequencies. I can use the LFO's for dubstep wobble effects pretty easily.
I've also been able to use the ADSR's controlling extreme noise gates while the envelope follower modulates cutoff.
I got pretty close to an OC-2 sound earlier today. The Axe-Fx's octave effect isn't as gritty as the OC-2 is, but you can easily address this by putting an amp simulator right after the octave effect, using one of zillions of EQ options available, filters, etc.
The pitch shifting and delay effects are easily just as high quality as the Eventide ones are. But now, I have way more flexibility, way more options, and even more delay types.
The modulation effects are really breathtaking though. The rotary effect is the most realistic digital replication I've heard. The phaser kills, and you can set the frequencies that it sweeps though to preserve as much low end as you need. The flanger is great as well. The chorus will let you modify the delay time and is definitely my favorite chorus of all time thus far.
There's only one bass amp model (SVT) but you can use any of the guitar models without losing any low end, and they all let you modify everything to your heart's content. The SVT sounds great right out of the box though. The tube overdrives that you can get with the guitar models are amazing... spine-tingling warm. Fractal definitely spent a LOT of time on these models. They all make Line 6, Boss, etc. sound utterly lifeless and I'm not missing my tube preamp at all so far.