Dave76
I have a 1st generation 18i20 that I absolutely hate. One of the worst musical equipment purchases I've ever made in my life. Completely unreliable. Crashes frequently, gets in a state over time where it starts dropping samples (i.e. clicking sounds), etc., etc.. I couldn't even begin to estimate the lost hours trying to get the thing to work not to mention all of the lost takes from it crashing. I've gone through countless audio interfaces from various manufacturers over the years and have never encountered any as bad as this one. Do some searching and you'll find others with similar experiences. Worst part is that they completely abandoned releasing officials drivers for like two years prior to introducing the 2nd gen. Obviously, quite a few people think their stuff is great and don't seem to have these issues but I'm assuming they are doing different things than I am so, as with anything, your mileage may vary.
I bought a first gen 2i4 and promptly took it back as "defective" but later learned that's the way it was designed. I hated the way the gains worked on the preamps. I had to turn them almost all the way up to get any gain and then it seemed like it "crossed over" to a different gain stage so the result was that there was one small sweet spot on the pot that worked, but anything else was way too little gain or way too much gain. on either channel.
got a Roland Duo and have loved it ever since! preamps are pretty clean for a low end audio device and the gain pots are smooth and linear. bonus: it doesn't come with a power supply, but you can use one with it instead of using the USB bus power!
the 2nd gen are supposed to be completely redesigned on the gain staging. I have no experience with the new ones.