After reading so many positive reviews on this thread, I gave the Aquila Alchemia normal tension a try. I'm a die-hard D'Addario EJ45FF (carbon) normal tension fan, so this review uses those as a basis for comparison.
After playing on Alchemia for a couple of weeks I think I might be switching. Here are the some key differences from EJ45FF:
Feel: The Alchemia trebles feel thicker, making their thickness more consistent with the basses. For some reason, my fingers really like that consistency. One downside of this extra thickness (on my guitar, with my action) is that I get buzz on the 1st string when fretting high and playing loud. The other big difference in terms of feel is a "tackiness" in the trebles, which makes it slightly harder to start a slide; but curiously, once the slide is in progress they feel very smooth to slide on. The net effect is nice: fretting fingers feel secure at rest, and glide well on slides. I've noticed this tackiness property feels slightly different on different days -- perhaps due to weather or the condition of my fingertips? Finally, slides on the basses seem less squeaky than EJ45FF, and they feel a bit thinner.
Sound: One big improvement in the sound is the consistency of tone across all the strings. With EJ45FF I've felt the different strings have slightly different characters, and it takes effort to compensate with the right hand and alternate fingerings. The Alchemia sound much more consistent across the strings --- it feels much closer to a single voice across the range. Another similar improvement is the consistency of tone across open and fretted notes: open 1st E sounds similar in tone to fretted F, whereas on EJ45FF the open string sounds more "harsh." Finally, the overall tone is, of course, different. Whereas EJ45FF sound like a buttery, even, strong voice, the Alchemia sound a bit more nylon-ish -- "hollow" is a word that comes to mind -- but unlike nylon, with a stronger attack and perhaps sustain. The Alchemia have a lot of character. The basses have a very nice, robust sound. One last detail: pull-offs on the trebles sound a lot stronger and fuller on Alchemia, and I'm wondering if the extra thickness is why.
Last detail is that the Alchemia take a long time to stretch to stable tuning, perhaps a bit longer than EJ45FF, but not by much.
Overall, I'm a bit fan. Kudos to the Aquila team!