Last year, I played in a couple playtest sessions with Gaming Ballistic, and I recently found the play reports while poking around on his blog. The test was for Dragon Heresy, which is an in-progress 5e clone that will no doubt be on Kickstarter and for sale one day.
(For those interested, Dragon Heresy differs from 5e in two main ways. First, the setting is in fantasy-Scandinavia instead of the Forgotten Realms. Second, it employs several variants the standard D&D combat rules, for example "vigor" and "wounds" replace standard hit points and armor acts as damage reduction instead of as something that lets you avoid getting hit altogether. It stands in relation to 5e in simultaneously the same ways that both Iron Heroes and Arcana Unearthed stand in relation to 3e.)
The first play report is here.
In the first session, the characters were tasked with recovering some forgotten crown jewels and documents proving something like the authenticity of the jewels and their hereditary connection to some current nobility.
I played a rune-casting barbarian, a new archetype from Dragon Heresy who can express dwarven runes while raging. (If I recall, most of the runes allow the barbarian to deal or become resistant to different kinds of damage. The other new archetypes for the other classes seemed cool and flavorful as well.)
The highlight of the session was fighting an angry hill giant. The revised combat rules mean that characters and monsters have more "vigor" than they would ordinarily have hit points, but they also have many fewer "wounds" - so attacks that directly target the wound reserve, which includes missile attacks, are more powerful.
The second play report is here.
In the second session, we fought a couple of wights riding ghostly horses. In this fight, the things that don't improve with level - the way that hit points and vigor do - worked against us this time. Another character fell off a parapet and nearly died from the fall, because "wounds" are fixed at 1st level, and falling goes straight "wounds" not "vigor." My character also nearly died from sheer exhaustion. Raging increases exhaustion, rune-casting increases exhaustion, (and possibly, being touched by a wight increases exhaustion) - and again, the amount of this a character can endure is fixed at 1st level. Running yourself ragged remains dangerous throughout your character's life. So despite the wights probably not being as dangerous as the giant, both our characters nearly died in this fight, because the same damage-rule asymmetry that we turned against the giant got turned against us this time around.
Those were the only two playtests that I participated in. Not long after I played, he launched a Kickstarter for a standalone volume of his variant grappling rules, which is now for sale as the book Dungeon Grappling.