Okay, we just finished a short first session today and I thought it might be good to post our impression. Please forgive me for any spelling mistakes, I'm a non-native speaker.
Since we spend some time reading the rules and looking at our sheets, the players didn't come that far into the adventure and we'll continue later this week, but I just figured I'd post our first impressions. To keep it short: we enjoyed it a great deal and thought the core rules were very fun and we liked the over-al direction the developers took with the rules. We especially liked the advantage and disadvantage rules, they added a lot of depth and variety to combat and the game as a whole.
Now, what did we do?
We were with 1 DM (me) and 3 players, who played the wizard, the fighter and the cleric of Moradin. We played on a grid, using dungeon tiles and miniatures.
The first encounter was a lot of fun, they faced a couple of the kobolds outside the cavern, within the woods. The wizard used light to disadvantage the kobolds, which made it very difficult for them to even hit the players. They continued to use this strategy and I was starting to get worried that it might become difficult for me to challenge the players (even with only 3 players). However, when they had entered the cave, the cleric and the wizard (with the light) fell into the pit trap, allerting a group of kobolds and leaving the fighter to deal with them alone. The cleric and wizard spend the first two rounds of combat trying to open the door and jump out. This time, it was a lot more challenging for them, but they defeated the kobolds.
At this point, the players decided to change their strategy a bit and the wizard cast light on all the weapons of the other players, making sure that all of them permanently had a source of light with them to disadvantage the kobolds. (Rolling two dice really increases the enjoyment the player had, looking out for which of the two was the lowest, in case of the disadvantaged kobolds).
Now, they quickly advanged, with all of the shining light sources. The fight against the rats was quick, easy and fun. Nothing special to say about it, really.
When the players elite kobolds though, things turned a bit. Since none of the players had thought about healing yet, each of them had around 4-5 points of damage. Since the elite kobolds had a higher attack score, the fact that they were disadvantaged didn't mean they'd always miss and the players had a lot of difficulty defeating them. When during the second round of battle, the Chieftain and his guards entered, all hell broke lose. The wizard used sleep, which allowed the others to kill a couple of the sleeping kobolds in the next two rounds, but the kobolds were with so many that the players were still overwhelmed. (At this point I realised I should've adapted the number of enemies a little to the smaller party, I consider this a fault on my part.) The wizard dropped to negative hit point and had some difficulty stabilizing. Luckily no kobold decided to coup de grace them (I figured they wouldn't do that, since the fighter attacked them and was trying to get their attention). The cleric managed to use his healing word and the players managed to kill all the kobolds, including the chieftain (critical hit by the fighter was very useful). If the kobolds hadn't been constantly disadvantaged though, I'm not sure they would've made it.
Now, at this point, the players had slaughtered around 20 or so kobolds, so I decreased the amount of kobolds that'd be in the common chamber to 20 too. The players spend a while in the Chieftain's chamber, healing and looting, and when they came out of the chamber, some of the kobolds had already come and see what had happened. With all of their shining weapons, the players chased the remaining kobolds out of the caverns and we called it a night.
So, to summarize: we had a lot of fun. Even though the adventure was a bit chaotic. First, I was afraid they might have too many hit points, but they didn't. They had enough to survive 1 encounter without being close to death, but they hadn't so much that they started feeling invincible, in fact they had to wath their hit points very closely. We had a great time and really enjoyed the rules. Being advantaged/disadvantaged is really important in this system, but that's okay since it's fun. It did worry me though that given that light is an at-will spell and kobolds are light sensitive, the players had an easy strategy to disadvantage kobolds, which for the basic "minion-type" kobold in my case meant that they stopped being a threat (unless in really large numbers or combined with elite guards or the chieftain). I'm sure that in many situations though, DMs can find solutions to counter such situations where players exploit easy ways to cause enemies to be disadvantaged (walking around with large glowing weapons, does tend to get the attention of monsters), so I don't worry to much about it.
I'd like to finish by thanking the developers for providing us with the playtest and we're looking forward to seeing the game develop in the direction that it now has. My players are looking forward to continueing the game in a few nights.
EDIT: I just found out that kobold's have a racial feature that gives them advantage if they outnumber the players... Wow... guess that would've changed the experience a lot. LOL.