So, if you are not a 4e hater, how would you rework it? My personal takes would be:
Well first I want to say that not including the half level bonus means that after a while you just really fall behind in your saves and skill. The half level bonus meant that you just got BETTER at being an adventurer all around as time went on. I would go for the proficiency bonus system of 5e because I like the variance in weapon proficiency bonuses.
A few things I would do:
1- Cut down on the sheer number of powers a character gets. Instant of just getting more and more Encounter powers you replace your previous ones with improved versions. I would replace the levels that give Utility powers with class features so that you could pick passive effects OR active powers (including skill powers). I would also make your class stop giving you stuff once you pick your Paragon Path and again with Epic Destiny. Maybe you just get extra uses of older powers. This would lower the choice paralysis in combat.
2- To further cut down on powers I would make it so a character would always only knows 2 powers that uses your reaction: basic Opprtunity Attacks and a class specific one with variable frequency. The Wizard would get Shield, for exemple, and maybe the rogue gets a reactive tumble, that sort of things. With a handful of races granting a third one (like the Goblin one that lets you shift when you're missed or the Halfling's power). Maybe some classes give you a few choices (that you could swap with retrain rules) but each character is hard limited so there's not a bunch of stuff.
3- I'd probably reduce the number of types of bonuses. Maybe down to "permanant" (maybe not actually permanant but with a fixed duration) and "temporary" (with a volatile duration) bonuses wth the highest one of each type always winning.
4- Maybe roll the buff duration mechanic with the Saves End mechanic. At the end of your turn you roll your saving throw, if you roll 11 or above you get rid of a negative effect on your of your choice, and if you roll 10 or below, you get rid of a POSITIVE effect on you. Sam would go for enemy. No more tracking of duration, you just roll a dice at the end of each turn and you could have mechanics that interact with that duration roll.
5- Personally I'm fine with the standard progression and format, but I would totally try to create mechanics that would thematically link the class of a same power source. I liked that Divine Class all had Channel Divinity, and I feel like all the others should have a similar linking mechanic.
6- Rework the Controller role so it feels more like a proper role and have the controllers more consistent.
7- Keep the Monster Vault math for monsters
8- Speaking of the HP bloat, I would reduce the max HP and up the number of Healing Surges a little bit. The goal would be to make individual battles more perilous while keeping the day longer.
9- Make more use of Rituals as well as the Disease Track.
Step 1: Exile whoever came up with Essentials to the MtG department, never to be seen again.
Good plan!