Last night was my group's first Spelljammer AP adventure, and I decided to ask if they'd be interested in trying out the new Nat20/Crit rules. 3 of the 4 players hadn't heard about the playtest, but after a brief discussion about it and ensuring them that we could go back to the 2014 rules after the first session, everyone agreed that it would be fun to try it out. One player (Warforged Paladin) was highly skeptical of the new rule (as was I when I first read about it) but was happy to try it out so she could give informed feedback on the survey. I thought the Rogue would also balk, but he was super into trying it out right from first mention. The other 2 party members, Fighter and Ranger, initially thought the rule sounded way better.
Nat 20 Results - 3 for PCs, 3 for monsters. Rogue had a sneak attack nat 20 lose it's crit damage, but also benefited from a Nat20 against him not getting critical damage. He then used his inspiration the very next turn after using his move and bonus to get close enough to a fleeing bad guy to attack (thus getting sneak attack) and took out the monster due to that. The Paladin also had a monster Nat20 and was thrilled to point out that my monster wouldn't get crit damage
The fighter and ranger were the other two Nat20s, both on weapon attack rolls, so both got their normal Crit damage.
Session wrap up - I'd already guessed given the reaction at the table to the various Nat20s thru the session, but the group enthusiastically decided to keep the rule for the remainder of the Spelljammer campaign, and are interested in incorporating other rule changes throughout when it makes sense to do so. The three players who just learned about the playtest are all also going to download the materials and participate in the survey.
For me, my last bit of doubt about the new rules disappeared after seeing them in play, and my initial thought that the Rogue specifically, and some other classes would need some new features to make up for the loss of Crit damage is now gone. The rule works perfectly fine on it's own. For example, the Paladin had initially planned on only using Smites when she Crit, but with the new rules used 2 smites at other moments, both of them the bonus action before attacking variety.
Would love to hear about other tables tales from this rule!