Roland GP-100

The interface is great, with analog controls if you wish to use them, and very useful shortcuts for getting to things quickly. Somebody put a lot of thought into this and it shows.
The manual is pretty crummy, even by Roland standards. They do have a few usage tips, but full effects descriptions are missing as are midi details.

Dynamite pre-amp. Covers the spectrum from AC-30 to Marshall to Soldano to 5150 emulation very accurately. I've heard decent solid state pre-amps before, but what sets this apart is the dynamics of how the sound changes over time and the sensitivity to attack, pickup selection, and volume control that is remarkably similar to a genuine tube amp. If you're not familiar with the GP-100, it uses technology borrowed from the VG-8 to arrive at its sounds.
The selection of digital effects is excellent, although it lacks a rotary speaker emulator. Some of the effects are skimpy in terms of the parameters you can control, especially the compressor, flanger, and chorus. And the reverbs, while of excellent quality, are limited in variety. Also, a number of the effects should have wet/dry controls, but don't...they're either on or off.
An excellent effects loop offers a workaround for any effects shortcomings. You can drop stereo send/return anywhere in the effects chain (in fact, the whole chain is user-modifiable).
I believe the dual feature is unique, where you can have two patches simultaneously and switch or continuously morph between them. In fact real-time control (via midi, or expression pedal) is excellent in general.

I spent months shopping, mainly comparing this to the GSP-2101. The GP-100 has a more faithful tube amp sound, with a similar set of digitial effects, plus the convenience of a single rack space solid state box.

The layout is simple and logical. From the having analog controls that you can tweak in realtime (even while you play, with a foot controller!) to the headphone jack on the front panel. Why would someone build a rack mountable module with the phone jack in the rear panel? Even though you can control every parameter of your sounds, there's very little need for it. The factory presets are so good you can take it from the box to the gig, take my word for it.

The thing sounds awesome! I'm not kidding, you can have the sound of Joe Walsh, Green Day, Van Halen and ... Boston! This last one had me drooling all over the place. I have the Tom Scholz (Mr. Ego himself) X100 Rockman but it doesn't even come close to how the GP-100 simulates that unique Boston sound.

No experience with reliability

No experience with Customer Support

If you're on the market for a guitar preamp/processor module, you should read this:
Hint: Get the Roland GP-100.
Mail Features: - Accurate emulation of many guitar amps and speakers - Analog controls in front panel: Bass, Mid, Treble, Pre and Post - 400 patches: 200 user, 200 preset - 22 bit (AF Method) 128x oversampling @ 44.1 kHz - Built in chromatic tuner
Pros: - Awesome, rich, thick and full bodied sound - Excellent reproduction of amp/speaker/mic combination including Marshall stacks (SLDN, 1959) and speaker cabinets (single/double stack, open/sealed cabinets, built-in, etc, Roland Jazz Chorus (JC-120), etc. Several mic. positions simulation - Many I/O jacks for effect loops (parallel), direct recording, etc. - Fully controllable via MIDI (not just patch changes) - Half height rack mountable - Excellent factory preset sounds
Cons: - Somewhat inaccurate data wheels - Two lines only LCD - Less than perfect owner's manual
Perspective:
I just finished a painful three weeks hunt for the perfect guitar processor. Results: the Roland GP-100. Period.
This machine has it all; incredible sound and ease of use. In trying to describe the sound I was looking for to the salesperson, I found a real challenge. I tried everything from comparing with some artists to try to make the sound with my voice. Yeah, you know, something like George Thorogood, Joe Walsh, Ed Van Halen; it's amazing how two people can hear the same thing so differently.
To heat up things a bit, let me compare the GP-100 to the GSP-2101; the module everyone is raving about lately. Did you know the GSP-2101 has the headphone jack in the rear panel .... hello, any body home?
I had the opportunity of having the GSP-2101 for two weeks for testing. I guess is a matter of taste but if you're Grunge head, the GSP-2101 is for you. Maybe you kids don't know or can't remember but Grunge sounds a hell of a lot like the psychedelic guitar sound of the 60's, at least to me (remember Fireball ...). The GSP-2101 has a fairly clear sound in the first three strings but when you get to the lower strings it sounds muffed and fuzzy, like singing with your mouth closed.
The GSP-2101 has no analog controls so, you can change the treble any time, but you'll have to go through several push button exercises. The preamp section order is fixed. This means that there's no way you can add wha or chorus the signal before applying distortion to it. The GP-100 does not have this limitation.
The GSP-2101comes with one processor, and unless you purchase a second processor (+/- $295), this unit is useless to live performances. You'll need the second processor to achieve what Digitech calls "seamless" program changes. This means that patches (effects) will change immediately after you depress the foot controller switch. With the GSP-2101, there's a noticeable gap between time you press the foot controller and when the unit actually changes the preset. And... you guess it, not with the GP-100.
Some folks prefer to have tubes in their effects processors. Why? Warmth, fullness and richness. The dynamics you can get from a tube is unparalleled. That is, a tube that has attained the right operating temperature and has the right amount of voltage through its filaments. Tubes need special care and handling; no heavy shocks or temperature/humidity changes. The bottom line of all this is the sound. Would you believe me if I tell you that the GP-100 holds its place in a one-on-one with a Marshall double stacker cranked up 3/4 of it's volume? even through headphones! Add to that chorus, flanger, delay, phaser, reverb, amps/speaker emulation, etc and you can't beat this beast. It's like having 2000 lbs of gear in a half rack package. Talk about compression!
Listen, I know it's very difficult to describe a sound, so if you're in doubt, I'll record a WAV file with some GP-100 presets and mail it to you! How's that for fan craze? Gee, maybe I should charge Roland for this stuff.
Whatever you do, listen very

This single rack space unit is my dream come true. Full midi control over almost every parameter. The manual is better than most Roland manuals I have seen (though) there's a few "written in Japanese and translated" artifacts.

The sound is highly versatile and realistic. I was going to choose between a SansAmp PSA-1 and Digitech GSP2101 but the Sansamp didn't have effects and the GSP didn't have enough preamp tweakability to my liking. This box has several amp emulations using the COSM technology from the VG-8 guitar system. They sound true to life. The effects are very clean and every parameter is adjustable. The 5 part intelligent harmonizer tracks well and is another reason I bought this unit. I'm amazed I don't see more on this on the Net or in the mags.

Looks pretty reliable to me. I just ordered a foot pedal so it will be easier to use live. Haven't had it long enough to rate this. So far, so good.

Decent support. There's one guy at Roland who is the guitar guru (forgot his name). His review of this unit had me salivating and he also answered some questions after I got the unit.

Love the unit: what do I like about it?: There's nothing that has the versatility of this unit that I've seen or heard for live or studio use.It has tone knobs for adjusting the preamp parameters. The preamp can act independent of patches or be stored as part of a patch. Huge diversity of sounds. Up to 16 effects in any order. 5 part harmonizer, tuner, and "VU" meter for any effect in the chain; Almost every item is addressable via midi; two separate stereo outs; 200 presets, 200 user slots.
I was stuck between going for the GSP2101 and the PSA-1 and found out about this unit. Those units are great, but for the all in one guitar box, the GP100, in my opinion, wins out. Strange how there is not more buzz in the press or Net on this unit, cuz it truly is awesome!