You are a trout

A little while ago my DnD group went into an arena battle in front of many spectators.  The rules were that each group could bring up to five members, but we only have four party members so that is what we went with.  Had we been really trying, we would certainly have found a fifth person to fill out the group, but we are slacking.

Our opponents were slacking worse than us though - they only brought 2 people.  2 Dwarven barbarians, specifically, who are really strong and tough.  They hit people with swords!

It turns out that being outnumbered and having a battle plan of 'hit people with swords' is not a good idea.

On the first round our bard turned a pile of coins into a bunch of summoned creatures to attack a barbarian.  The barbarian dodged the animated coins and bashed the bard for a little bit of damage.  Then the other barbarian charged me and his attacks bounced off my magical defenses, me being a wizard and all.  So far, little was accomplished by either side.

Then our monk punched a barbarian in the head, stunning him for a round.  Then I turned the other barbarian into a trout with Polymorph.  We then spent the next two rounds beating on the stunned barbarian, who kept being restunned each turn until he died.

Our party sat there, staring at the trout that used to be an angry barbarian, laughing. 

Eventually the organizers called the match in our favour, without us having to go through the embarrassment of beating the last barbarian into a pulp.

This is the thing that a lot of DnD folks call 'action economy'.  Our group got more actions than the enemies, so we won.  I don't think that is a useful description of the real problem though - the real problem is the way parties get more and more ways to completely disable opponents as they level up.  Getting lots of actions isn't a huge problem as long as your actions don't instantly win the fight! 

As your damage goes up, so does enemy hit points.  As your attack bonuses go up, so does enemy armour class.  This works to increase challenge while keeping the system working the same.  Unfortunately the spells that permanently remove a combatant get more and more powerful without any counter.  We also get more spells and ability uses so we can just pour on low level disabling effects if we want to.

Of course stuns and Polymorphs aren't the only effects we can rely on.  Later on that same day the two dwarves decided to get their revenge and so they jumped us as we were sleeping and attempted to kill us.  Our bard cast Calm Emotions, which made both the barbarians stop wanting to fight, and our druid cast Suggestion, making them think that it was a great idea to go away and not fight us anymore.

So they did.

It is nice to be tough and strong and all, but when a single failed save removes you from the fight completely it just isn't enough.

In Heroes By Trade I removed all combat effects that did things like this.  Combat effects are temporary, and while they scale up to do some pretty cool things they never have 8 hour durations and force the opponent to leave the battlefield!  I think DnD does have some advantage in terms of flavour, of course - people like having all kinds of crazy spells that you can use on a moment's notice.  Unfortunately it causes problems like this - encounters that should be epic and memorable become a simple matter of a single spell and a single failed save.