Some thoughts about the campaigns I've been in recently, or at least the rules used for each:
Fabula Ultima: I really liked how the introductory one shot breaks the pre-made character sheets into numbered stages, with a story structured to let the GM introduce each section in turn. This is brilliant, and feels simple and intuitive - every game should do this. I also like that the system has enough depth in character design, particularly with its obligate multiclassing, to give players a huge amount of flexibility to turn their RP vision into something playable without being buried in math. The JRPG framework is giving us good expectations for player driven storytelling and world building - we've got a fair bit of silliness, but it's not outside the bounds of JRPG tropes (Jungle Scots! Dinosaurs! Flying islands populated by British assholes!). I'm quite excited about my character and the campaign; I've deliberately set myself up as a driving force when it comes to activity, which is new for me.
Stonetop: just finished session zero for a second Stonetop campaign (sessions for the first being sporadic), and it's such a fun process. The baked in collaboration is wonderfully stimulating; you take a group of strangers with their own ideas of who they want to play and how they want the game to go, and all of a sudden everyone is latching into everyone else's story, and a campaign starts to emerge. Where the game could improve this process is the playbooks - they cover all the things they should, but they are not structured to support the linear session zero process the game appears to prescribe. I would like to completely rearrange them, and perhaps move the collaboration forward a bit. Tonight's game was a three player group, which made the Q/A stuff a bit intimate at first, but once we got going it was surprisingly productive. I think everyone has a pretty coherent view of our game world, and now we have to find a way to gel these particular characters into a party - but the GM has assured us that threats abound, so I'm sure it will happen. This will be fun. I really do like how the playbooks drive thinking in terms of being part of the village's community, rather than just Rando the Munchkin's latest McGuffin.
Dungeons and Dragons, Fourth Edition: we wrapped up our 4e experiment a few weeks ago; the system was better than its reputation suggested, but it was still badly overburdened by mechanics and alien vocabulary. I liked how all the powers were put through a standard template, highlighting all the key facts without burying them in distracting cruft (or fiction, as the proponents would call it). I didn't like having to learn new terminology to parse them. I had a great deal of fun building characters (so many vivid characters!), but the role system (You are a striker and you will like it) was needlessly heavy-handed and off-putting. The designers clearly drew from MMOs and turn based tactical games, but... really dated ones. If that gameplay style wasn't what you want, you're gonna have a bad time.
With the emphasis on grid and math, the game functionally requires a VTT to play properly - and VTT support for dead systems is somewhat lacking. It's too crunchy for its own good - the designers clearly wanted players to collaboratively RP crazy action movie scenes in combat, but in the process they buried the players in so much goo that figuring out what they can do and when is the only thing on their minds. There were lots of good ideas in the system, especially with regards to non-combat things and skill challenges, and I could see a fully modernized version being fun for crunchy play. On the other hand, none of the strong bits require putting up with the technical debt of trying to play a complex and unpopular ruleset that was dropped ten years ago for a reason. That said, it was a fun experiment, and everyone wanted to keep playing their characters (even if none of them wanted me to keep playing mine).
Thread through all of this: enthusiasm is infectious, and collaboration hastens its spread. Rules should encourage player agency and engagement with both the game world and one another. Players and GMs should be on the same page about what they want to get out of a campaign - storytelling, story writing, number crunching, ERP, whatever. Please don't invite me to your ERP campaigns.