I am a huge fan of epic play. To quote one of my own quotes (as vain as that may be), "I thrive on needless complexity." And nothing is quite so complex as an epic level build.
But somewhere along the way, the developers seem to have decided that "Epic" means "Outside of the domain of balance." It's true that 4th Edition is far more balanced than third edition ever was at epic, but I'm often left wondering "what were they thinking?" when I see a class feature or power that's above 23rd level. Though honestly, with some classes, it's not even limited to that high level, but I digress.
There is an inherent thinking in most people's minds, in my experience, towards wanting to start campaigns at lower levels-namely, level one. The reduced complexity means it's easy to get into the game and play from scratch, and it allows for more room to grow. But campaigns are finite entities, and advancement is relatively linear. In short, the higher level something is, the less often you're likely to see it in real play. Which means the less playtesting it gets. So when something at epic is nerfed, you can pretty much bet it's because it was just flat-out broken.
By far the worst offender in this department is the aforementioned level thirty. After all, when you're 30th level, why are you still playing? You've maxed your XP, and have only one level's worth of treasure to gather. Perhaps you wish to beat the crap out of Tiamat. Which shouldn't be hard, considering you're laden with the features I'm about to describe! A lot of destinies also have overpowered 26th level utilities, but that's a bit different of an issue, and almost universally is limited to 1/day (which because it's "Only a Daily" means it doesn't count, am I right?)
It's the Top X of Y overpowered Epic Destiny 30th level features list! You'll notice that a lot of these destinies are of the "WTF that's worthless" variety if you were to ignore these features. Go figure-I guess that constitutes "Balance."
Glorious Spirit (Bearer of Doom): Reading over this, I was really blindsided. On the one hand, you'd think it'd be relatively useless-after all, who wants to miss with a power, right? But it's actually really quite insidious. Bearer of Doom works in junction with any single target power-including daily attacks. Here we have a good way to get unlimited rages, unlimited heals, unlimited who knows what! All you have to do is attack unarmed and you're fighting at -9 to hit. Throw in Power Attack for good measure and you're at -11. If you can figure out any other way of crippling your attack bonus, that goes a long way. Also useful for when you want to hit-Storm of Blades comes to mind
Arcane Sword (Spellsword Perfection): Holy Frack on a Frackertonbox. Whatever that means. Arcane Sword is the quintessential "Playing for 30" Epic destiny. Level 21 is mediocre (roughly equivalent to an average epic feat), 26th level is utterly useless, and I've no idea how to interpret 24th level-does your sword automatically win the battle, since it can't be attacked? But the Coup De Grace is At-Will Lightning Bolt Charge. And let's be frank-there's maybe one or two other powers that are even remotely as useful, but under virtually all circumstances? Lightning Bolt Charge is where it's at. Deal more damage per round than a ranger! Unless said ranger managed to find one of these epic destinies. What's great is that this one feature can take a build that has no viable at-will attacks-because it has no Intelligence based attacks and only multiclassed Swordmage-and give it a viable at-will option. It's absurd.
Archlich (Essence of Undeath): You know, to be honest, I don't even know if this is overpowered. It feels overpowered to me, but that's a bad barometer. It doesn't really belong on this list-at least not as long as I'm keeping Archmage, Archspell, and Lorekeeper off the list. Still, with the Archlich's autoplinkage of minions, a bard lich can have a crapton of heals per encounter. Fair warning: due to the unique dynamic they incur, Rules As Written disallows an artificer from actually being able to use this feature to regain Curative Admixture uses. Go figure.
Avangion (Avangion Rising): Who needs leaders anymore, am I right? With a Ring of Tenacious Will or, hell, just playing a shielding swordmage, you can always get up to twenty surges per day. Not that that much matters, seeing as how you can just use a ritual to trade surges back and forth between encounters. Avangion Rising wouldn't be even remotely overpowered if it weren't for the fact that, unlike Invincible Mind and War Master (the latter of which is actually a leader destiny), it does not require an immediate action to trigger.
Ceaseless Guardian (Never Again): This has a similar problem to Avangion but probably shouldn't make the list for two reasons. One, unlike Avangion, the healing is flat surge value, not Surge value +Ability Modifier. Secondly, it doesn't help you unless you're preventing death. I know that seems like it's small but really, if the entire party falls unconscious, as long as no one actually dies, they'll remain unconscious. You can't use Never Again to really keep your DPR up most of the time. Ceaseless Guardian deserves honorable mention for having the same issues as Avangion, but honestly it probably doesn't deserve being on this list.
Cosmic Soul? (Cosmic Connection): You know, I look at Cosmic Soul and don't really see (snark snark) it as an overpowered destiny. But honestly, all attacks are Range Sight? Imagine using a telescope to blast away with magic missile. This one is definitely a widget technique, so it gets an honorable mention. In practical play, the feature and rest of the path are mechanically next to useless.
Dead God Avatar (Sacrifice): I really hate to have all these borderline issues. With Dead God Avatar, it's not overpowered at will, but for at least three encounters per day, you can basically have unlimited encounter attacks. Imagine using Tumbling Strike every single round. Or more practically, Sever the Source. The surge cost makes it only useful for limited builds though, so don't expect this destiny to be ruining too many games.
Elf High Mage (Empowered By Life): Another widget build. This time, it involves having someone willing to trade surges to you after the end of every encounter, again seriously reducing the practicality of the power. But being to automatically get yourself a critical hit can't be ignored. After all, imagine a Basilisk Soul monk automatically critically hitting and petrifying enemies left and right. If nothing else, using the feature to trigger a healing daily power means that the end cost is virtually nill.
Magister (Magic's Master): Did you know that there's a ritual that gives you the effect of an extended rest? Meaning, once per day, you can gain the benefits as if it's tomorrow. I'm reminded of how a 21st level Wu Jen in 3.5 could use Persistent Time Stop. Aside from the blatant exceptions though, it's not a big issue.
Perfect Slayer (Perfect Killer): This is probably one of the most absurd features on this list. You take a multiclass feat that gives, at best, 2d6+12 damage per encounter (well, maybe not at best) and turn it into a class that lets you deal 4d6+24 damage per attack. If you have brutal barrage, Bam-your damage per round just got upped by 16d6+96. Yes, that's 152 on average. This is almost exclusively useful against solo monsters mind you, since you'll only be able to place your shroud twice, and only one of those will max that to four shrouds. In addition, if your DM is using the Cleanser rules for solo bosses, don't expect your shrouds to last even that long. Though, it's time to invest in a way to regain an encounter utility power (if you can find one).
Planeshaper (Shape Reality): This power is only "Totally awesome" on its own, but when you consider the possibility to "Box in" enemies without any attack roll, saving throw, etc-that's when the sheer brokenness kicks in. Not as effective against huge or larger enemies though.
Punisher of the Gods (Bringer of Dooms): How does this interact with Vorpal Weaponry?! In any event, maximum damage is a whole lot like getting an automatic critical hit. Just imagine the synergy with Rage Strike. Though a more practical approach is for an Executioner to try it out-your encounter attack now deals +90 damage. Cool story bro.
Saint (Golden Halo): As if divine healers weren't already insane enough, now you have the ability to heal an additional 25 HP. Unlike every other source, this isn't surge specific. Meaning that Astral Seal does, in fact, still heal about 35 or more HP.
The sad thing is that, most of the paths that didn't make this list, really do kind of suck. Oh, there's a few exceptions-Archspell, Archmage, Demiurge, just to name a few. But it just seems like someone decided somewhere down the line that 30th level is for suckers. Go figure.