The more I use the 2120, the more I appreciate the sound. It is basically split into two sections, the preamp and the effects. I love the effects. Great reverb (use it in stereo!), delay, etc. You will find lot's of pleasure here. There is no shortage of quality. The only ones I have been really disappointed in are the auto wah and envelope filter. But overall, Digitech gives you tremendous control over the quality effects. I also like being able to program the control-one foot pedal, turning effects on and off at will.
The preamp side is what shapes your tone and is what I consider the hard part. Let me begin with some background information (forgive me if I sound preachy.)
First, if you are recording direct with the 2120, it sounds fantastic. You can easily manipulate the tone and it will sound great. I would venture a bet that digitech created the unit in a studio, making it optimal for direct recording. Run it stereo, you'll be happy. (note - the 2120 offers an amp simulater which is supposed to shape the overall sound for direct recording. To my ears, it's nothing more than a low-pass filter of some kind. But it does help.)
Now, playing through your amp is an entire different story. Get to know your amp first. I recommend running your guitar directly into your amp and set the tone (duh!). I mention this because before you spend hours programming the 2120 (and you will), you have to be confident in your amp settings. Ultimately, your amp is going change the tone of your signal. Therefore, spend days getting to know the nuances of your amp and guitar! Then, once you are totally satisfied with your amp settings, you can add your 2120 in the chain and begin the process of finding your tone again! You will notice a change is sound immediately. Frankly, getting back to the natural sound of your guitar/amp is not easy, even if you bypass the 2120. Because it is a preamp, it changes the tone of your guitar and you must go through the process of building your sound.
The overdrive and distortion on the 2120 give you a wide spectrum of tone and sound quite good. However, they go hand and hand with the EQ. That means, you will be spending a lot of time adjusting the EQ settings to get that tone you like. (Some have recommended changing the tubes in the 2120 for better tone, something I am considering doing.) It has take me a while to get comfortable with the distortion/eq options but I am finally enjoying the fruits of my labor. You might find the overdrive/distortion a little dis-tasteful at first, but keep in mind that you must program the EQ. I have come to really enjoy the sound of the preamp.
Following the distortion/EQ settings, the 2120 has a solid noise gate that comes quite handy for controling noise and buzz. You'll like this.
Remember, the 2120 is basically a digital unit. The sound can have that plinky digital quality to it if you're not carefull. But you can work through it with eq settings, etc.
Final thought - One reason I bought the 2120 was so I could change patches without a drop-out in sound. This a little deceiving on digitech's end. Basically, the way it works is that the effects from the first patch will hold-over (overlap) with the next patch. For some patch changes it works great. Others, not so great. There is still a little delay time in the change... but maybe I'm being unreasonable.
I bought the 2120 used and I did have problems with reliability. What I discovered was that the foot-controller was broken (thanks dude!), which was causing the system to crash! It was ugly for a while. I had to buy a new foot-controler and it has been very reliable ever since. I also replaced the battery inside the 2120 (bought from radio shack) while it it was down.
There is a person on the internet who offers a great free software download for backing up your patches onto your computer. This person is a God-send. He deserves to be given lots and lots of money. I highly recommend this download. (note - when backing up your patches to a computer, unplug all of your cords from 2120 except your midi cables.)
Overall, I love the unit. It lives up to its billing. The price is reasonable and you have a ton of effects, features, and options. Just keep in mind you will be spending a lot of time programming with this one. You have to work for your sound. It will take time. Are you on the fence? Go ahead and buy it. You'll like it, with time.