What if leveling was focused solely around adding creative options for players - rather than scaling? Instead of adding so many pluses/minuses, let the players do something they weren’t otherwise able to do before. I think there is a kernel of coolness here, if you’re willing to read on.
Let’s get rid of number bloaters that give us the illusion of advancement (BAB, save progression, items buffing attack/damage/stats/saves, increasing spell variables, etc.).
If a Fighter class granted a flat 40 HP (+Con Mod), +3 to all attacks, +3 Fort saves, these numbers would remain that way his entire career and be meaningful compared to a Wizard forever having 16 HP (+Con Mod) and +3 saves vs. spells. Whatever the numbers are, the gist is that these formerly variable ever-increasing numbers become fixed regardless of your level. The 40 HP vs. 16 HP is a 2.5 ratio, which one could argue is more-or-less the design intention of giving a d10 HD to one class versus d4 HD to another.
But the cool stuff that makes the game fun is to add player options! And I’m not talking about more 4e power cards that all basically do the same thing, and a process that gets repeated every fight (blow through encounters, stuck with boring at-wills in a fight that drags on forever). Make the focus of the game all about the cool class features, and how they bend or break the core rules.
Each class should get at least one cool class feature every level (or better yet, to pick from a list of cool class features unique to the class, like SW Saga Talent Trees, or Monte’s Akashic from Arcana Evolved). Players can only ever be in one class. Instead of multi-classing, let WotC release new classes in supplementary books that are, in-and-of-themselves, effectively a multiclass. This lets them continue to make money on add-on products, still maintain control over combinations so they don’t become too powerful and (if WotC released enough interesting new classes) still appease players that like offbeat combinations.
You can further customize and make your PC unique in other already-established ways. Pick a character’s Background, to provide their “level 0” fluff and benefits. With less (or no) bloat, these should also be significantly more meaningful throughout their entire career.
Make feats more general in nature, either available to a group of classes (i.e., former “martial” classes) or to any class. There are no such things as feats that have pre-requisites of a single class (those would be moved to within the class itself, as class features/talent trees). I’d do away with any feat that contributed to numeric bloating (dodge, weapon focus, etc.) and instead just let them bend/break core rules to grant players more options during play. Perhaps dodge lets you force a foe to reroll an attack as an Immediate Interrupt once per fight, or simply let you roll 1d6 and add the result to your defenses for one turn a fight. Feats that let you take arcane area effects (such as Fireball) and create safe unaffected pockets to avoid hitting allies, or halve the radius to double the damage.
Skills are either known (trained) or unknown (untrained), but don’t have escalating bonuses to deal with escalating DCs. Trained provides a flat +2 bonus to the roll. Ripping off Pathfinder a bit, any class can train in any skills they want, but you get flat +3 bonus to any class skill you are “trained” in (incentive to train your class skills). You can pick up “skill training” feats to become trained in more skills as you advance. Tack on the ability modifier. Fighter Str 18 (+4), plus trained (+2), plus class skill (+3) = +9 total. Done. That number stays that way for the rest of your career, and the only way to boost it were crazy rare or infrequent/temporary.
I would imagine you could easily build a balanced skill DC table around this, making the +9 bonus a very good chance to succeed at athletics checks in general. And for anything else, you can create class features or feats without resorting to stacking bonuses. Just rip off all the cool utility powers from 4e. For example, you could have feats that let you jump twice as far as normal, exceed normal limits, treat it as if you made a running start, climb twice as fast and so on. Feats that let you bypass DR/hardness while smashing down a door. Feats improving knowledge checks by letting you roll twice and take the best result.
Ability scores stay the same your whole career. Only exceptions should be crazy rare (artifacts, Wish-like effects or campaign climax). I’ve got no problem with Str 18 being the human max. It also makes the racial ability modifiers more meaningful, instead of them being buried in a pool stacking numbers that get you beyond a 30 stat. Damage bloat also being gone, your Str 18 fighter is doing 8 points of damage on average with his longsword, dropping a foe (of equal level) in 5 hits.
A single HP is meaningful now. Another crazy thought is to keep HP as being nicks/fatigue-based, but treat healing surge boxes as “wound” boxes. Once a character drops to 0 HPs, the character suffers a real wound (put an X in a wound box), is bleeding and falls unconscious. I.E., your HP are a threshold for a wound. Like SW Saga, let there be a spell to heal the HPs (frequent and easier to cast, brings ally conscious, stops bleeding, back into the fray) and a separate “cure wounds” spell that removes wound boxes (which can only be cast outside of combat, harder to cast or fewer per day). All the other iterations of healing HPs still exist (inspiring words, second wind, etc.), since HP is still potentially a restoration of morale or ignoring fatigue. Have wound boxes bestow conditional penalties of some kind, but not so extreme that a couple wounds neuters you into being unable to participate in combat.
You can have classes factor into quantity of wound boxes as well as severity of wound penalties. Barbarian could inherently have more boxes, allowed to suffer more wounds before he starts seeing penalties, and even then, a much more forgiving penalty progression when they start appearing.
Once your wound boxes are all X’ed off, you’re dead (last box being the fatal blow). Nice side-effects: no more negative HP tracking required here (0 HP or less is simply 0 HP and unconscious/bleeding) and a small handful of temporary hit points become cooler in this setup. Throw in a few ways to bypass HPs and deal a wound directly (critical hits, the former save-or-die stuff, a few rare monster abilities).
To represent differing experience/power level levels between creatures (i.e., level 1 fighter goes up against level 10 fighter), I’m sure there are plenty of crafty ways to handle this. Off the top of my head, you could simply take the difference in levels between combatants and add it as a bonus to the higher level creature’s base damage/attack/defenses (and possibly even things like damage reduction). If your team of 5th level PCs go up against a 5th level orc, use the orc’s stock numbers since he is the same level as the PCs. But if the PCs go up against an 8th level ogre, simply add +3 to all the ogre’s numbers to represent the difference (yes, I presume all PCs are always the same level as each other; it’s just how we play).
As an aside, I like the concept of limiting the spellcasting by connecting it to HPs. Casting is fatiguing; it costs you HPs to cast a spell. If you toss enough, you wound yourself and collapse unconscious. Very dramatic. I think SW Saga did something like this. I’ve always disliked the huge number of D&D spells out there too. Way too many. I’d prefer a significantly smaller list of spell choices and make each one cool, and let class features and feats modify them in interesting ways to give more options.
And to the above a well-crafted adventure to introducing the circumstantial stuff and variability, and of course, a good story.
Not saying it's perfect, but does it have promise? What do you think?