An interesting discussion just started up one of my game threads. The player in question mentioned that I run extra-hard monsters - and that the way to counter them was not so much to have higher defenses, but to pick powers that interrupt their attacks or smack them with an effect.
That intrigued me, because he's quite right, but I hadn't thought of it in precisely those terms before. I thnk of myself as a complete softy as my kill rate is extremely low, but I look at some of the encounters I've run recently and I do see what he means. The monsters are tough to deal with. There are probably a couple of reasons for that, but I'm now eager to hear other experiences.
When I'm designing (or tinkering with, in the case of pre-written material) an encounter, I am rigorous about the XP budget allocation. I'll often push it as far as I think it can go, but I will never deliberately outface a party. More often though, I aim for a middle ground. Tough, but tricky/bypassable with cunning/feel-good killery (yes, it has a place, not often, but it does. Sometimes heroes need to feel awesome).
Note that I'm not set in stone about how encounters will end. If the players take a route that allows or suggests that the bad guys may change sides, surrender or run away for reinforcements rather than simply battling to the death, I'll take it. Golden rule - combat is storytelling too. My drama head is never that far away.
I'm raising this point about XP budget because it is an extraordinarly flexible and very effective tool for determining if the party should or should not be able to cope. It is by far the best yardstick I've found and hasn't failed me yet. Mechanically it helps hugely. What I do tend to do however, is shift the numbers a bit. Typically I like monsters to have lower hit points and higher attacks and damage. They won't stay around as long, but they'll be devastating until the party get rid of them. It's a good incentive for the party to act as a party and decide where to focus their fire.
On my side of the coin, I try to make it hard for them to decide where to focus their fire. That enormous lumbering bod may be able to knock 30hp off you if he hits you, but the real danger this turn might be the agile chap at the back who can push you into a pit and leave you as easy pickings for something else. Synergy works for monsters too. This is a large part of why I like intelligent monsters better, although a mixture can be very good.
Some favourite fights?
The kenku who had a group of gelatinous cubes buries all over the floor and dragged the party into them.
The fight in the hotel lobby (long story) that ended with the baddie being killed by a thrown pot plant.
The epic fight to quiet the land at the end of one group's heroic tier path. It was massive to play and run, but was appropriately epic feeling as a rite of passage.
A recent fight with wraiths in Tomb of Horrors which was on a real knife-edge right the way through.
The fight at the end of Courts of the Shadow Fey against the Moonlit King and his followers. That ended when the King was forced out of his madness, but not before most of the party were very badly beaten up.
I think this one is to be continued. Many thoughts are burgeoning.