My 4E campaign currently has characters at levels 24-26 (depending on how many sessions the players have missed) and adventuring through an epically up-scaled version of the Crater Ridge Mines from Return to the Temple of Elemental Evil. I actually managed to kill a PC in the last session, which partly came about because my upscaling of the monsters might have had the damage just a little too high, but I can live with that. And so can he, as the group had access to Raise Dead. (Sadly, he was a couple of levels short of the "when you die" power...)
This was the statblock in question. Oops.
CHIMERA: L27 Elite Brute, 22,000 XP, large natural magical beast; Init +19, Perc +22
HP 614, AC 39, F40, R37, W37; Resist 20 fire
Speed 6, Fly 12; Save +2, AP 1
All-around Vision: can’t be flanked
Dragon’s Bite: Melee 2; +32 vs AC, 4d12+18 damage and ongoing 10 fire (save)
Lion’s Bite: Melee 1; +32 vs AC, 4d8+26 damage
Ram’s Gore: Melee 1; +32 vs AC, 4d10+22 and prone; push 3 if chimera charged
Triple Threat: attack with all 3 attacks
Dragon Breath: (5,6): close blast 5, +28 vs Ref, 3d10+27 fire and ongoing 20 fire (save)
Bloodied Breath: when first blooded, breathe.
Str +22, Con +21, Dex 19, Int +12, Wis +17, Cha +19
And yes, that's exactly how the stats looked in the Word document I've compiled with the monster stats.

Again, we were using the Dwarven Forge tiles - some of which I've primed, and which I'll move to properly painting over the next week. (I've got a few doors done, and they look great). In the picture above, the dwarf is actually a foe - the Bullywug he's menacing is one of the heroes! (A bullywug monk, picked up when the group was investigating the Tomb of Horrors in the Vast Swamp).
One of the interesting things about this game is that although there are a couple of problems with the underlying maths, they aren't that bad and a few tweaks to the monster stats has fixed up most of my problems. Thus giving me fun sessions at 25th level. I've also run a 4E game to 30th level, and it's the only system I've been happy running at these levels. I'm using the idea that the Crater Ridge Mines are infused with elemental energy as to why the monsters are so tough, and the idea of stopping the manifestation of Tharizdun is definitely an epic-tier adventure... at some point, the ending of this adventure will diverge from the printed adventure, but I'm happily adapting at the moment.
I am running some big combats, though. The tiles actually filled even more of the table than I've shown in the photo, and foes were coming from everywhere. Mostly minions, but epic-level minions are still fairly scary - even if most were dying relatively quickly, they were drawing attacks from the important foes. My biggest problem at this level is from players who are really slow at basic maths. Rolling 5d6+40 shouldn't take 2 minutes to calculate! These big set-pieces can take more than 10 rounds (and between 90-120 minutes to resolve) but mostly they're flowing well around the table.
My biggest problem with powers comes from one from the Psion that inflicts a -8 penalty to attacks of creatures in a burst 1. It's just way too big a penalty, and stems from the problems with the Power Point system for psionics. (The power in question is Dishearten: augment 2, burst 1, penalty equal to Charisma bonus, which is then augmented by a feat). At 2 PP per use, that's entirely too many rounds of usage for an epic-level character. The solos I send them against now basically ignore it (along with stunned and dazed, although my fix is generally to make them spend an AP to get rid of the effect). I really like what 4E did with psionics (I spent a very happy 10 levels playing an Ardent), but there's a few rough spots I'd probably revisit if I start another campaign.
It's actually a little hard to tell what system I'd use for my next campaign for this group. 5E or 4E? The group has really been enjoying 4E, and they may well not want to change to 5E. In any case, the other games I run will allow me to see how 5E goes, once it is finally released.
Cheers!
This was the statblock in question. Oops.
CHIMERA: L27 Elite Brute, 22,000 XP, large natural magical beast; Init +19, Perc +22
HP 614, AC 39, F40, R37, W37; Resist 20 fire
Speed 6, Fly 12; Save +2, AP 1
All-around Vision: can’t be flanked
Dragon’s Bite: Melee 2; +32 vs AC, 4d12+18 damage and ongoing 10 fire (save)
Lion’s Bite: Melee 1; +32 vs AC, 4d8+26 damage
Ram’s Gore: Melee 1; +32 vs AC, 4d10+22 and prone; push 3 if chimera charged
Triple Threat: attack with all 3 attacks
Dragon Breath: (5,6): close blast 5, +28 vs Ref, 3d10+27 fire and ongoing 20 fire (save)
Bloodied Breath: when first blooded, breathe.
Str +22, Con +21, Dex 19, Int +12, Wis +17, Cha +19
And yes, that's exactly how the stats looked in the Word document I've compiled with the monster stats.

Again, we were using the Dwarven Forge tiles - some of which I've primed, and which I'll move to properly painting over the next week. (I've got a few doors done, and they look great). In the picture above, the dwarf is actually a foe - the Bullywug he's menacing is one of the heroes! (A bullywug monk, picked up when the group was investigating the Tomb of Horrors in the Vast Swamp).
One of the interesting things about this game is that although there are a couple of problems with the underlying maths, they aren't that bad and a few tweaks to the monster stats has fixed up most of my problems. Thus giving me fun sessions at 25th level. I've also run a 4E game to 30th level, and it's the only system I've been happy running at these levels. I'm using the idea that the Crater Ridge Mines are infused with elemental energy as to why the monsters are so tough, and the idea of stopping the manifestation of Tharizdun is definitely an epic-tier adventure... at some point, the ending of this adventure will diverge from the printed adventure, but I'm happily adapting at the moment.
I am running some big combats, though. The tiles actually filled even more of the table than I've shown in the photo, and foes were coming from everywhere. Mostly minions, but epic-level minions are still fairly scary - even if most were dying relatively quickly, they were drawing attacks from the important foes. My biggest problem at this level is from players who are really slow at basic maths. Rolling 5d6+40 shouldn't take 2 minutes to calculate! These big set-pieces can take more than 10 rounds (and between 90-120 minutes to resolve) but mostly they're flowing well around the table.
My biggest problem with powers comes from one from the Psion that inflicts a -8 penalty to attacks of creatures in a burst 1. It's just way too big a penalty, and stems from the problems with the Power Point system for psionics. (The power in question is Dishearten: augment 2, burst 1, penalty equal to Charisma bonus, which is then augmented by a feat). At 2 PP per use, that's entirely too many rounds of usage for an epic-level character. The solos I send them against now basically ignore it (along with stunned and dazed, although my fix is generally to make them spend an AP to get rid of the effect). I really like what 4E did with psionics (I spent a very happy 10 levels playing an Ardent), but there's a few rough spots I'd probably revisit if I start another campaign.
It's actually a little hard to tell what system I'd use for my next campaign for this group. 5E or 4E? The group has really been enjoying 4E, and they may well not want to change to 5E. In any case, the other games I run will allow me to see how 5E goes, once it is finally released.
Cheers!