I've been using D'Addario NYXLs for years now and my review will be mostly centered around comparison with them. They were my go-to strings for pretty much all my guitars, the only problem I had with them is that my sweat appears to be acidic which would turn the strings rusty within a week and tone-dead after about two weeks—sure, they lasted longer than a set of regular EXLs or regular EB Slinkys but not enough to justify the price difference. They were saving me some time as I didn't have to change my strings as frequently which is why I continued to use and recommend them but I wanted strings that I'll change once a month! With ~1hr / day playing on average, I don't think that's too much to ask.
I tried various coated kinds including all Elixir types, D'Addario's own EXPs, even some gold-plated ones and they were either too mellow or too slippery... never really felt good about any of them. Plus many of the 'coated' ones lasted even less than the NYXLs, they just wouldn't appear as rusty but they would get tone-dead just as well.
Step in the new XT line. They are advertised as NYXLs with extended life due to the coating which you will not notice under your fingers. Is it true? Largely—yes!
There is a tiny tactile difference between NYXLs and XTs but you will be able to notice that only if you compare them side by side (as did I only when I restrung a fresh set on another guitar). They also sound virtually identical (at least I cannot notice the difference) which is another thing that was always putting me off from coated strings.
But do they last longer? Oh boy, do they! I currently have them set on my most frequently used guitar and they have been going strong for 3+ weeks! They do sound a slightly duller than a freshly put set of NYXLs but it's been 3 weeks and they are still not tone-dead! Meanwhile they look as NYXLs I've put on 3 days ago (I'd attach a picture if possible) which just blows my mind.
So, there you have it—XTs are my new favorite, I do still have quite a stash of NYXLs to go through but pretty soon I will be replacing all of my strings with XTs. D'Addario has hit a jackpot with these!