See, I am no expert, so actually couldn't give any "correct impressions". Still a few things the way my ears hear.
First these are very different IEMs. I believe if you like RE0 you will not like RE1 and vice versa. RE0 is detailed, analytical. It's colder and brighter. Highs are extremely detailed extended , more detailed than TripleFi. Bright IEM would mean it's a bit fatiguing.
It has "got bass". I would completely disagree with anyone who suggests these don't have bass. Of course, no big fat bass. But when amped bass is detailed, deep and punchy. Slight mid bass hump in some of the tracks.
mids are very detailed, but dry and analytical. Vocals are good but nothing great. soundstage unlike a few, I find it ordinary even amped.
RE1 is not detail oriented, it's about smooth lush mids. Vocals are very good, far better than RE0. After RE1 you would hate RE0 vocals. Violin, flute,saxophone, piano sound excellent. It has got good highs, better with my sparrow. It's dark definitely, but you don't need to search for highs. Perhaps, sparrow being hot in highs might help RE1, but frankly, I didn't find sparrow to be hot even with RE0. It has got excellent soundstage, width is great.
Bass is pretty good, better than RE0. It's tight controlled, deep and punchy, has got impact too when needed. It goes really low. But only when amped. I prefer RE1's bass to anything else I own, I believe it has got the right quantity. Some disagree. Dont expect loads of bass, it's not TripleFi.
Most importantly it's non fatiguing sound signature allows you to hear them for hours, unlike RE0 or TripleFi. And never expect any sibilance frome RE1. To me that's great as I am very sensitive to sibilance unlike many. None of my friends seem to be bothered with sibilance, not even with Hippo VB.
Personally I prefer cold, thin, bright IEMs, so my personal choice would be RE0. Only issue being vocals. I would definitely get something which would be great for vocals.
Why do I like RE2 a lot? I think it has got the right brightness. It's neither too bright nor dark, just right. It has got very good vocals, forward mids is what I personally like(inverted V). It has got "natural" bass to my ears. And yes, for it's price good soundstage too. Good clarity and details. Perhaps the right amount of brightness and very good at vocals seal the deal for me.
I listen to pretty ordinary music, mostly contemporary popular music, most often badly recorded. RE0 does get sibilant with these. RE2 doesn't, even when they actually are bright and has got forward mids.

Hope this helps.
