About the mana regen thing, here's my reasoning:
1. Previously we had two systems for making powerful spells slow to cast: mana and cooldown. That's redundant, a little confusing, and mostly just annoys new players with small spells.
2. Mana, it seems to me, would be more interesting as a "do I have the capacity to cast this at all" sort of meter. That's something that doesn't overlap with cooldowns at all.
3. For the next week, my most ardent concern is the new player experience -- making the new player experience fiddly so that the hardcore players get something more fun later is a Really Bad Idea (tm). At PAX it was really apparent how frustrating it was to get that "not enough mana to cast X" popup a bunch. It's simply not any fun, and 100% definitely had to be fixed.
4. I look at balancing stuff like this almost like a chemistry equation. When you change one side of the equation, then it puts the other side out of balance, sure. So now we have some problems at the upper end. But at some point you have to pick some variables that you say "these are fixed and are now correct, and we'll balance the rest around them." When you keep shifting all the variables at once, it's really hard to come out with a balanced equation.
5. What I mean by #4 is that the new player experience has to be good -- and therefore the mana regen can't be painfully slow from the start. End of story. We're going to frustrate people left and right if we do that, and so we just simply can't do that. This is our fixed variable: mana needs to regen pretty darn fast, there's simply no two ways about it... so now it's time to balance the rest of the equation around that.
6. My rationale is that, contrary to some of my prior thinking, there's not really any good reason to use mana as a limiter as how frequently you can cast the smaller spells. If you look at most Metroidvania type titles, you get infinite shots with your basic stuff. I think we had too many spells where you had to be overly conservative of mana because of their rate of usage.
7. Going along with that, however, I think we still have too narrow a spectrum of spell mana costs; which is right in line with what you were saying, Terraziel. We need more of a spread in terms of mana costs, which will do two things: 1) it will make certain spells closed off to low-mana characters; 2) it will make it so that the high-mana characters who want to use those spells actually get right back into the situation of having to watch their mana a bit and be careful, because while the regen rate has been doubled, if we double the mana costs of a spell then we're right back to where we were before with that spell.
8. So you can almost infer that nothing changed from #7, but that's not right either. The difference being that suddenly we have a lot more variety of spells: stuff that is cheap and infinite-fire and that anyone can use; stuff that is middle-cost and which a lot of characters (but not all) can use, and which works more or less like things previously did; and stuff that is substantially higher-cost and where a high-mana character with the mana-regen enchants is going to be a really interesting new kind of glass cannon; and then finally the really ultra-powerful spells (of which we currently have none), where perhaps only super-high-mana characters can even cast them all, but they are devastating when they are used.
9. The trouble is, as I noted in the release notes, I've not really added those other spells yet, and nor have I gone through the current crop of spells to shift them around much.
10. Oh, and cooldowns are still around and are all kinds of useful for the mega-spells, too. We already use pretty long cooldowns on these for the summons, but for really powerful spells we could do some pretty crazy stuff with these. The worry of being able to spam a mega-spell because of mana regen rates is not actually something to worry about, because cooldowns give us perfect flexibility on that front.
TLDR: My goal is to both make the new player experience smoother, and actually to give more complex and deeper options for advanced players at the same time, and I think that the changes so far are a really solid step in that direction. I hate making players play one way, and the mana balance was getting in the way and making a lot of things feel same-y that shouldn't have.