The run I've been playing most recently (not my most recently-begun run, but it is my only extant game at the moment) is one of the best I've had in quite a while: Half-Orc Fighter of Gozag, I've got enough AC, SH and resistances at my disposal where only the mightiest of individual hits can do much to me, and enough money that I could (if I needed to) bribe some of the tougher branches which remain. Even in the Vaults (so far) and the Depths (which I've now cleared while putting off tackling the bottom floor of the Vaults), almost nothing has made me have to slow down and think, "Okay, I need to take this a little more carefully." But Vaults 5 has killed enough of my strong characters who've made it that far for me to not be able to be cavalier about its danger, so I'm definitely going to bribe the branch again (my previous bribery fund for it having been exhausted), and buff up with a couple potions before going down there.
Still not sure if I'm going to attempt to go for any of the more optional branches and/or runes before going for the Orb, or just call it and go for my third win ever; I suppose it will mostly depend on how well/badly Vaults 5 goes.

Wish me luck, fellow delvers!

I've died over a thousand times (2000?) and never won. It really irritates me, and while I love fantasy, I dislike how mages/magic work in the game, and that I've been killed over and over and over. Many if not most of those deaths I blame on poor documentation or the game outright cheating. Games cheating ruins the fun for me so I'd like to never play again but, like an addiction, I'll eventually fire it up again, and die again, and ragequit again.

Well, I got through Vaults 5, with a lovely vacation in the Abyss partway through that made V:5 itself seem like a pleasant diversion by comparison. Wound up chugging all my heal wounds potions (and using Gozag's Potion Petition ability several times as well) just to survive, but I spent a large majority of my time there at <50% health. Somehow, I found myself on the deepest level of the Abyss (I didn't pay attention to which layer I started on after my banishment, but at least once, I took a portal to a deeper level just to get out of a dangerous situation), and I wound up getting the Abyssal Rune by happenstance before I could find and successfully use a portal back to the Vaults.
And it wasn't till after I had been banished that I realized I had completely forgotten to re-bribe the Vaults before I descended to V:5! -_- (Sadly, the denizens of the Abyss are apparently above accepting graft.) And by the time I got back, I figured I'd already cleared enough of the enemies that it would've been a waste of money to do so then. No matter, my stack of scrolls of immolation and my overall rF++ meant I had little problem dealing with the mobs I got swarmed by before and for a short time after my vacation. I mean, I also have a halfway decent artifact main weapon (double sword or double blade, whatever the base weapon type's called) and, as mentioned, gobs of armor and shielding -- and reflection, which I forgot to mention before. That's been kind of important, too. :D
Now, before I go...wherever I'm gonna go next (still haven't decided, though after the time I had in the Abyss, I don't think I feel like checking out the Hells or Pandemonium), I have to remember to check my mutations and see if there's anything worth dealing with. I got malmutated at least a handful of times in the Abyss, and after the first couple, I kinda stopped checking, and I hadn't gone into V:5 with any potions of mutation (and DCSS v0.20 is the first version where the effects of the older potions of mutation, beneficial mutation and cure mutation were combined into one, which I believe is still the case in recent builds), so there was nothing to be done at the time; and by the time I got out, got up to Vaults 4, and got rested, I had more or less forgotten about that entirely.

What about the spellcasting do you not like?
What kind of documentation do you think the game is missing, or what parts of the existing info do you find insufficient or misleading? (I assume you're speaking of the in-game help info. I have my own thoughts on some things that could be expanded on, but it's mostly to do with a total lack of explanation of some of the technical terms used with regard to the in-game search function and in the options guide; I find that most of the info on actual gameplay systems is not only decent, but often better -- and almost always better-written -- than info in a lot of paid games. And from what I've seen of more recent versions, there seems to have been a noticeable increase in the amount of numeric, mechanical info provided to the player over the last several years.)
In what way do you think the game's cheating? (I'm aware of at least one or two ways in which the enemies and neutral/allied creatures work differently from how the PC works, but the only slightly "cheaty" part is that they're somewhat implied to work differently than they do, not that they're adapting based on info they shouldn't have, or suddenly using equipment they neither spawned with nor picked up, etc.)

Being killed over and over is part of it being a Rogue-like. :) But if you want to practice without fear of death, there is a Wizard mode you can enable -- I believe the keyboard shortcut is "+" (as in, "Shift"+"="). I've never messed with it, but I remember it exists because of how many times I've accidentally almost enabled it when trying to do something else (thank Trog for that "Are you sure...?" prompt ;P ). I think it invalidates that run from being counted in your high scores, or something.