I disagree with the game finishing at 20, but that is just a matter of preference. That is if I'm understanding correctly your use of apotheosis as the completion of the character's (group's) destiny quest. I would simply have made Epic a 3 or 5 level progression instead of 10 levels (levels 21-25 are Epic, for example). 10 levels is hard to fill out, and Epic can drag if not enough is happening, IMO.
Yeah, I thought about that too. I've considered that maybe there should be say 18 levels of regular play and then 3 levels of Epic, with level 21 being a 'capstone' where all the crazy gets to REALLY hang out. That would be cool too. I thought 10 levels of heroic was OK, 10 levels of paragon was fine too, though I'd be OK even with say 6,6,3, which would be 15 levels total. I just sort of thought 20 levels was a bit of a nice nod to classic D&D, since level 20 is usually thought of as the 'endpoint' of character progression in most versions of the game (yeah, I know, not all, and technically all classic D&D is 'open ended').
I do agree with the removal of cruft - powers and feats. The idea of swapping powers was one that made little sense, though mechanically it was understandable why. Powers should simply scale better or have gradients with level. Redundant feats, should be culled, and more feats should be generalized so that they don't have stupid restrictions and can be shared instead of creating similar feats twice or more. On the other hand feats could have also been made to have more versatility so that they grow with the character. So a feat you pick at level 3, has more effects at level 8, etc. At level 8 you choose the new effects, or pick another feat. Things like that.
Totally agree on the use of the disease track. I've done this extensively to great effect in my game. Rituals on the other hand I'm a bit on the fence on. That is one area of the game that could really have broken entirely with the base framework and I would not have even batted an eye on. I think that one of their weaknesses is that they tried to standardize this area too much. This more than anything is what creates the whacky costs and other weirdness. I could have seen these become the "high magic" component of the game. Rain of Colorless Fire, a ritual - cost unknown/undefined.
I think you COULD in 4e have those sorts of rituals. They're not REALLY character resources though, they're more like plot devices. Though different from artifacts they serve a pretty similar purpose, something that shapes the narrative and may benefit the character, but is really ultimately its own thing. 4e to me always did a much better job of suggesting these things than other editions too. AD&D always seemed very 'guarded', like the advice on anything that wasn't in the book was "be suspicious, restrict it, don't give players an inch" but in 4e it was more like "well, here's all the really nailed-down stuff, now, when you want to open up a can of crazy, just go for it!"
Magic Items I can see the reason within the design space, so I'm not extremely bothered by them. For example the items in Mord's Mag Emp are more interesting than those before, but I can see design space for the wide range. With 4e I liked that they really made it so Magic Items could completely be an optional thing by using the Inherent Bonus.
How would you have corrected/improved what you mention about tactical insufficiency, which I'm not totally understanding?
Well, I just think that 'tactics' in 4e was very much centered on timing power uses, combining things into combos, and finding ways to front-load your firepower with things like interrupt speed attacks and such. Surprising someone is decent, but its not a BIG advantage. Terrain CAN sometimes be pretty handy, but in reality lying prone and sniping with a crossbow from the cover of even a small elevation is stupid awesome, yet it gets you a 5 point AC bonus, at most, often nothing. Attacking someone from higher ground? Nothing. Setting a weapon against a charge? Doesn't even exist, you can do the Ready Action, but there's no such thing as setting a pike. There's no system for loyalty or morale either, which is too bad. I think these things should be central to tactics, that is REAL TACTICS like you'd practice in REALITY. I don't want to eschew the cool fantastic elements by any means, but I would like to SHOWCASE them. The coolest moves tend to get buried in a heap of trivia. I think the 4e devs saw this too, as over time they tried in places like Essentials to pare down powers both in number and to a standard of more simplicity and more effect. I think you see the same thing with 5e's various class features in a lot of cases.
This would also help with certain problems that exist in 4e with combat. For instance, right now suppose a bunch of weaker enemies ambush the party. Its fun for a round or two, but pretty soon the PCs have got their actions and its just a fight against weaker enemies, somewhat time-consuming but trivial. Make surprise really mean something, more like it really does, BAD NEWS, and all of a sudden a group of weaker opponents isn't something to scoff at anymore if they get a jump on you. Sure, you'll win, and probably win pretty quickly, but it should be SCARY and make you blow some real resources to compensate for.