They dealt over 400 damage to this foe, all of the spells were completely ineffective, and as mentioned above the weapons were only 25% effective for the most part. This battle combined with another one where the Ranger in the group was scouting ahead, about 50 feet in front of the party was surprised by a Behir. The Behir only received it's surprise round and one other round of attacks, even on the surprise round having swallowed the Elven ranger whole, it never made it to the 2nd round of combat.
Granted, at first I liked the fact that D&D Next had quick battles (especially compared to 4E), but after awhile they were just too quick, even for complex battle where I'd actually pull out miniatures to make sure the players knew what was going on, it was hardly worth the effort as it was over before it really started. I do like the AC changes, where they are lower and that the combat bonuses slowly increase and begin around +4 to +6 for the party at low levels.
Players would seldom even bother to think before entering a battle, the attitude was, "Sure my weapon deals 1/4th damage, but this fight will be over soon enough." This got me thinking, what was missing? I even started adding more resistances to creatures where it made sense, like Undead gaining a resistance to cold. I was attempting to get the party to think before rushing into battle, what really seemed to do the trick was granting creatures damage reduction (DR).
As an example a Fighter with a Great Sword vs Silver Dagger going up against a Werewolf. Without Monster Manual (not being available until next month) I have no idea what the actual stats are on a Werewolf, so I'm making them up here to demonstrate how using resistances, vulnerability and DR changes the battle.
Granting the Werewolf resistance to normal weapons would cause the great sword to deal (2d6+3) / 2, or 5 on average per hit. The dagger, even if it dealt normal damage would be d4+3, or only 5.5 on average. This would hardly make it worth it to go through the effort and expense to carry around a silver dagger, even if the players knew Werewolves were in the area. However, by adding vulnerability vs silver to the werewolf changes the story. With this the average damage with the silver weapon is twice that of the great sword. Further granting the werewolf a DR of 2 cause the Great Sword's average to be reduced to 3, where DR does not apply to vulnerable attacks, so the dagger remains at 11 which is nearly a x4 (using average damage) over the great sword. Now that's worth having.
In the above example, a creature with all three resistances, vulnerabilities and damage reduction (RV&DR) clearly shows the benefit of not only going through the extra trouble of finding a weapon that exposes the creatures weakness, but even in the extreme great sword vs a dagger, it's over three times more effective using the dagger. This is the type of game mechanic change that I was looking for, one that exposes how useless always rushing into battle with the same attack can be, versus thinking about how to best effect the creature encountered, then using that to your advantage.
I also really wanted to reduce the number of opponents required to make a battle challenging, so rather than me having to use three ogres, because factoring in the damage per round of the party and the hit points of an ogre, the "mathing" it all out and guessing that with three of them it will grant the ogres 6 to 8 attacks on the party before the party finishes them off. Reducing the number of opponents by adding RV&DR does increase the complexity of the reduced number of creatures, but it also reduces having to track more of them and gives the party less to focus on as well. The goal could be realized by granting damage reduction and giving the ogre a cleaving attack (because why wouldn't it be able to swing through an arc of heroes?).
Then three ogres could be replaced with a single one, that is a much more dangerous opponent where the creatures DR might reduce every attack by 5, causing only "good" attacks to get through. This puts characters with magical powers into a more critical into defeating such a the creature, where the tanks are more put into the roll of simply stopping this hulk from getting to the other party members, with the majority of the melee attacks on such a creature be ineffective, though not completely as character's attacks in 5th edition typically are in the range of 2d6+3 damage (or basically [Weapon] + 3 for Attribute + d6). Magical Weapons would grant a Penetrate of 2 (on average), thus a magical sword vs the Ogre in the hands of a 16 Str Fighter would exactly overcome the DR of 5, allowing for straight weapon damage to be rolled each attack.
For many battles the addition of DR will likely not have much of an effect on the speed or actions of the party, as bandits or the like will only have a DR of 1 or up to DR 3, though likely no vulnerabilities or resistances. However for fantastic creatures, like ogres, giants, umber hulks and of course dragons, adding DR along with a special ability that grants them some type of multi-attack or area of effect attack makes these creatures all of the sudden a force to reckon with or something that requires them to change tactics. No longer is every just everyone essentially performing their standard "at-will" power...Though, when added DR you likely will have to scale AC to an appropriate number. For example, Hobgoblins AC 18 (chain+shield), should likely be an AC of 16 DR 4.
Two more things to add...I admit that all my data on was gathered from the alpha/beta versions of D&D Next, and so some creatures may have already been altered, possibly with the resistances and vulnerabilities that make sense that they should have, or their hitpoints and damage may have been altered such that granting them too much DR turns them into a TPK machine, so take the above advice with caution as you explore the new 5th edition.
Taking the time for the party to use things like fire or other environmental effects to their advantage will become important in their situations when their weapons are not as effective as they want them to be. Though don't forget the party also has DR, typical values might be Leather = DR1, Chainmail = DR3, Platemail = DR5, with shields granting either +1 AC or DR2.
Looking at it this way it is clear that a Paladin in platemail with an AC of 19 and DR of 5, is an impossible target for say goblins to touch, so the additional change that needs to happen is the drops by half the value of the DR granted (like the Hobgoblin example above). So in this case the Paladin's AC would be 16 (the same hold true for dragons, but Ogres with an AC of 11 probably wouldn't need to change Ogres might need to in fact go the other direction to a 13AC). The thought being they are easier to hit, as their bulk slows them down, just the attacks are less effective. Also, kobold/goblin tactics would change, they would likely have one of them aid another one, granting them advantage on their attack, this attack would then attempt a called shot (see above, with disadvantage canceling the advantage), thus over all it halves the number of attacks on well armored foes, but the damage on the successful attack would go from (d4+2)-5 to 2d4+2 (using kobold damage here).
The DR can be situational as well, such as heavy boots vs caltrops or leather gauntlets vs poison needles, but this would only matter in cases such as Orc barbarians that aren't wearing much, if any, armor, but have their thick heavy steel toed boots, and the party Druid casts Spike Growth...Then the 3 DR of their boots would help them vs the Spike Growth damage.
This way I can tweak the mechanics along the way, most of it is not that hard as I created "Monster Stat Cards" of all the creatures for the session, including party members and I have all the notes on them, plus its not a big deal if I forget DR sometimes, and attribute it to a lucky shot. I'm sure many will view this as an unnecessary complexity, but it seems like a fairly easy way to add additional realism into ones campaign, especially if you're seeing the same thing I was seeing in the beta of D&D Next.