A couple of folks here have expressed an interest in some details on the Zoom G3 so, after a few days acclimatisation, here we go. This is quite long but there's a lot to cover.

First, what is it? Well, it's a multi effect with all the usual stompbox and amp sims with a very simple 3 slot layout and knobs for editing. It also has a basic drum machine, a 40 second looper and all the ins and outs you would expect.
Construction is mainly metal with a solid diecast main body and a steel baseplate and feels as sturdy as an overgrown Boss pedal. The foot switches are metal and positive in operation. The knobs are recessed below the three lcd screens.
There is a row of lit buttons above the displays for extra functions. It can be powered by the supplied mains adapter, 4 x AA batteries or via USB. The power switch has an "eco" position which will turn the unit off after 25mins idle time.

Switch on and you're faced with a "home" screen showing the individual effects from the last patch used. Holding down the left switch takes you into patch mode. The other two scroll up and down through the patches. Pushing two switches at once will scroll up or down banks. Simple and effective.
A button takes you to a "global" menu for master volume, output selection (direct, combo front, combo loop, etc) and USB settings.

In "home" mode changing an effect is as simple as pushing the type buttons followed by a bit of knob twisting for parameter editing. All in all very quick. A "total" button takes you to the patch settings where you can change patch level, expression pedal assignment and (most useful) effect order. Want your tape echo before your amp sim? Twist a knob and it's done. Prefer the way it was? Another twist to put it back. That's about it for editing.

Settings are saved as you go along and the patch "remembers" which effects were on when you exit "home" mode to select another patch. In practice this means you can set up a patch for a clean sound with an overdrive assigned but switched off. Hold the left button after selecting the patch and kick in the OD as required. Cool. Patch switching is very fast. I can't detect any delay.

Want drums? Push the rhythm button, twist knobs for patterns, tempo and volume. A push on a foot switch takes you back to the effects selection.

It boasts the usual set of ins and outs. There is an pad button on the input if you have a very hot guitar. As well as stereo 1/4" sockets ,the L doubles as the headphone output, there is a balanced mono XLR. This has a ground lift switch (handy) and a pre/post button to send a direct signal out through the XLR while using the jack for effected signal. You will have to choose between a foot switch or an expression pedal for external control. Personally I'd use a foot switch for tap tempo on delays only. You needs may be different.

OK, so what does it sound like? Most of the effects are as good as any I've heard in a multi-effect. The choruses and delays are very good and quiet. The drives are pretty convincing and distinct. There are a load of wacky filter effects if you want to do synth impressions (it is a Zoom). Some of the factory patches illustrate the possibilities of the more out there fx nicely.
My main doubts are around the amp sims. They all sound very bright to me. Fortunately they all have 4 band eq. I'll listen to them a bit more and report back.

On the downside, you only have 3 effect slots. things like EQ and noise reduction take up one slot each. However nearly all the individual effects have a tone control and most of them are pretty quiet. High gain amps and drives are the only things you'd need to use the gate for. Also there are some combined effects so you can have say chorus and delay together in one slot.
Some effect combinations will reach the limit of the DSP. The unit will mark the unusable effect with "thru" if you try to select an unsuitable combination. You can't use two amp sims together.

I need to practice more with the looper but it certainly works and you can use the drum machine at the same time.

Plugging it into my Macbook Pro it appears in the audio preferences as an input and output device. Windows users will need to download an ASIO driver.
I spent a jolly hour or two this morning playing along with some tracks in iTunes monitoring through headphones plugged into the G3. Balance was easy to set in the "global" menu and sound quality was fine through my budget Sennheiser 'phones.
There is a computer editing application which works pretty well. You can export patches for sharing too.

Is it worth the money? Oh, yes. Does it have limitations? Oh, yes! But overall you get a lot for the price and I can't fault the build quality and user interface. I'd say it's even easier to use than the Boss ME-50 I had a few years ago and you can change to fx order on this one.

At this price and size you could put it on your pedal board to cover time based effects and a few "special" patches along with your favourite drives and wah for little more than the price of a decent delay pedal and you'll still have capacity left to use it for headphone practice with amp sims, looping and as an interface to a DAW. Phew!

Any questions? Ask away...