I own about a dozen of their libraries. Their guitars in particular are beautifully sampled and extremely flexible. I expect to get a lot of use out of them over the years (although I don't care for their strumming engine.) OTS customer service is top notch.
I bought a bunch of their libs during their yearly group sales. Very hefty discount, and you cam add additional discount via their savings system, check it out.
Great company, maybe the best guitars out there, for solo work. I too don't like the strumming system very much (that is: I csn't get my head around it). Piano is due for an update though.
The developer Greg has responded personally to every enquiry I've had - top notch customer service, and their guitars are stellar (I have the Acoustic Slide & Lapsteel). Looking forward to V2 of their Rosewood Yamaha C7 grand which is in the works
My favourite developer, I have literally everything he's released except mind control and the two new basses (but they will be mine, oh yes they will be) and I have not been disappointed by anything. The man takes pride in his work clearly making VIs he'd like to use himself with high levels of quality control rather than just rushing out new products, is constantly updating his older guitar libraries to match his newer guitar libraries, has very friendly and responsive customer service, and is incredibly generous with his bundle discounts, sales and reward points (orange slices) which can all be used in conjunction with each other.
My favorite guitar libraries are by OTS and Ample Sound. They both have beautiful recording and scripting, but they are very different, so it might be useful to hear about those difference.
Orange Tree Samples Evolution guitar libraries come with a lot of effects, and the developer creates stunning presets. All of these are previewed in a video like this one.
As soon as you install it, it's like you immediately have many different guitars. You might think you could get something similar by running it through effects in something like Guitar Rig, AmpliTube, but these effects presets are wedded to the way the articulations and other things are set up for the instrument. I feel that these presets were painstakingly and lovingly created to bring out the best in each specific instrument. This feature puts them in a class of their own.
Within the setup you can choose among 4 pickup positions, pick style and position, and not just double tracking but up to quad multitracking. It's amazing the options and how beautiful they sound. The presets in the video suggest this, but it is better when you have the library because each one plays differently.
They also have a lot of articulations, and a very easy-to-use user interface for setting them up for your own presets, including the usual keyswitching (reg and latch), but also velocity range, sustain pedal, cc change, or even random.
It's very good at recognizing the guitar chords based on what you play on the piano.
The big weakness is in the strum engine. It's just very limited and not very realistic. If this is ever improved, the OTS Evolution series will be perfect.
Ample Sound also makes high-quality guitar virtual instruments that rival or better the OTS ones. I only own an acoustic, but in that one, the focus is more on getting the best out of the standard sound of the guitar, rather than treating it with a host of effects. (It may be different with the electrics) It comes with a very elaborate EQ, Compressor, Delay, and Reverb. These effects have visual displays similar to what you see in plugins, not what normally comes with an instrument library.
My Ample Sound library can also be customized in many ways. The main difference is that it takes a bit longer to figure out how to use it. OTS libraries are easier.
But my Ample Sound library shines with strumming and fingerpicking. It has several ways to get a realistic strum or finger pick sound. One is similar to what you find in other libraries--a lot of presets--but another, which AS calls the Riffer, is pretty extraordinary. You can get amazingly realistic effects out of it if you know what you're doing, but if you don't, there is a fun randomizer.
The good news is that the patterns in the Riffer can be dragged into your DAW, so if you have one Ample Sound guitar you can use all of the patterns you generate in OTS libraries, albeit with a bit of editing.
While I have never had a single problem with my OTS libraries, I have had a question or two. When I sent a note to the developer, he wrote back immediately. The answer he gave was so honest that it actually cost him money in the short run, because I decided not to buy a library, but to wait. He lost my money in the short run but he gained my loyalty as a customer forever.
Neither did I when I first bought it. No matter how I EQed it, the piano was a bit too muddy-sounding for my taste. I contemplated selling it. But then I was writing a pop song that needed a darker, full-sounding piano during an interlude, and the Rosewood fit the bill better than all my other libraries.
I have their guitars and i use them a lot. I find them really great and best for leads, plucking etc. But im still learning how to use them for strumming becoz i couldn't get a decent strumming out of them mainly for acoustic guitars. Looking forward to pick few more this year. And btw their customer service is awesome.
Edit: There is a video for strumming from OTS which sounds good. Have to try it out.