He makes some interesting points, I made some comments on the blog but I'll reiterate some of them here.
Criticals: Critical hits from PCs on multiple attacks are most adequately countered with triggered actions (no-action and free especially). Something that on a hit can whack back against a PC to knock them away, or lets the monster shift out of reach or similar. These powers can be countered - immobilize for example prevents a monster from shifting - so they aren't entirely cheap "metagame" tactics (plus they'll work on non-crits anyway). It means the party needs more set up and therefore, more overall tactics to make their big powers work. Instead of them being a given every combat.
Stopping this sort of thing and making criticals not reliable "You're dead" is about terrain and monster design. Terrain makes getting into position more difficult, provides cover or concealment, allows monsters to heal or even get extra triggered powers (or whatever else). By epic PCs should be besieging their enemies in their own homes: But by extension that should mean the monsters have everything their own way.
Monster Design: I noticed a lot that many were complaining they forgot monsters powers and similar. This impacts the encounter heavily and it's so vital to remember what your monsters do. The less you miss and better you understand how they work the better. This is more work though and is far from how simple heroic/paragon is in comparison complexity wise. But think of it this way: PCs have to remember a host of specialized conditions, bonuses and similar as well by epic. An individual monster can be complex, but 5 monsters - especially if you use the odd duplicate - isn't terribly complex.
It's important to mix together complexity. Not every monster has to be complicated, but it's important that you have those strong monsters around to back up the others. Creatures from MM3 and beyond are brilliant, they are complicated enough they can put up a real threat while not being overly so.
Solos and elites, who rely on keen understanding of their powers deserve extra time on their turns. Don't be afraid to think about what to do for a moment: You are not a computer. You are not expected to move as soon as your turn comes around as the DM. If you need time to think of what to do, check a monsters powers and such do so. It's better to spend a minute to recollect your thoughts and think about how a monster functions, than feel disappointed because that push 1 (if you'd remembered) would have stopped the Barbarians string of 4 crits after the first one.
By far the biggest reason I see for post-MM3 solos not being challenging is DMs simply forgetting auras or triggered actions. These make up a very important part of current solo monsters.