I have actually not tried the Greyhawk Initiative system, but I have tried the similar Speed Factor Initiative and liked it quite a lot. What I found was that, contrary to what one might expect upon reading that you re-roll Initiative every round, it actually sped up combat a lot. That was actually the main benefit for me, as there was very little slowdown from players trying to carefully weigh options on their turns. I found that players losing actions due to their declared action no longer being possible was actually very, very rare, however it was quite common that players would get to their turn and say, “Aww man, I wish I could do X instead,” but always knew exactly what X was, so I added a house rule that you can choose to Ready an action instead of taking your declared action. This didn’t cause an noticeable slowdown, so I kept it. I noticed that in this system players use options like dash and disengage far less often, so I’ve considered experimenting with the Greyhawk Initiative system and having those options add dice instead of costing an action, but I haven’t tested that yet. I would also not want to use either option with a group with players who aren’t very experienced with D&D. The primary draw for me was the way it sped up combat, which I don’t think it would do if the players weren’t all very familiar with all of their spells and abilities. That’s why I’m not currently using it, because my group right now has two brand new players and one player who has only played online and isn’t used to doing everything analogue. Ultimately, it’s a useful tool in the toolbox. If you and your players don’t mind a little added complexity, it’s definitely worth a try, but it won’t be for every group.
