The big issue for me in Open is the TERRIBLE performance that can occur if someone with (I assume) either a particularly poor connection or low-spec PC enters an instance. Several times when I was last playing in Open regularly, I'd be happily playing - perhaps in a HazRes for example - and would suddenly start experiencing poor game performance, ships rubber-banding, hits not counting and the like, only to notice another player had just entered the instance. This ruins the experience totally, with the only option being to relog.
Compounding this issue is the degree of entitlement of some players when it come to PvP interactions, and the resultant toxic comms when you don't want to play "their" game the way they demand. Even just managing to escape might be poor form from their perspective, and you'll get abuse for not standing and fighting - in your unarmed trade ship lol. I had a combo of the two during my last interaction in Open. I was flying a trading configured Anaconda to a station for outfitting (Note, I thought I was in mobius, so not paying close attention, my bad). Got interdicted and insta-attacked - only "roleplay" here is murder, I had no cargo or bounty nor was I aligned with any power - however, the performance of our mutual instance (I submitted) was soo poor as to become unplayable. I can only assume the other Commander's connection or PC had problems, as his ship appeared to be able to teleport and not take damage - indeed, he appeared in front of me when we entered the instance after I submitted, and was shooting right away. My own ship did not initially appear to take any damage from a volley of missiles, until my shields (the only strong, well-Engineered module of the ship, transferred from another vessel) insta-depleted. 100% to 0% in a fraction of a second. I then appeared to get some sort of weird UI freeze - I've seen this before when there's (what appears to be) a network issue between players / server - and I was basically out of the game, unable to interact with my ship. I had to MENU log as I could no longer actually play. Returning to the game, I attempted to message the other commander, explaining what went wrong, but they just did the usual "stick to solo, learn to play wahh wahh wahh" . No acceptance of the TECHNICAL problem that caused the instance to crash.
This one interaction totally and utterly put me off going into Open. Not been back since.
Conversely, when playing in Private Group - either my own, or Mobius - and instancing with people I know to have good connections and PC's, we can fly around for hours with our SLF's deployed and get flawless performance, while engaged in heavy combat, be it a CZ or Res site. With this being the norm - I usually team up with friends in-game - having another player showing up degrade performance so much is a bit of a shock.
The thing that I don't like is how a PvPer ganker - i.e. someone who bravely preys on ships that have no chance vs. them and no roleplay reason (outside plain murder) to attack that ship - can force their gameplay on whatever unsuspecting player they want with zero practical consequences. The crime system in ED is a total joke. Now, if I could shoot a ship with my magic "trade beam" and force them to make 10 profitable trade runs in a row, then we'd have some parity lol. Seriously though, if a player murders another player that's clean, not in an anarchy and not on an opposing PP faction etc., then the punishment should be more severe.
I used to love flying around in Open, just to see other commanders. Most interactions were great, a quick o7 over the comms. Loved that. However, to have an entire relaxing gameplay evening wrecked by toxic interaction. Nope, I don't need that. To be clear, I did not object to being interdicted, though the lack of legitimate motive (outside of murder) is something I found a little odd - I don't really get the motivation to force someone into PvP who's evidently NOT flying a combat ship, isn't wanted, isn't carrying valuable cargo (a Pirate wouldn't bother) etc. Then add the terrible performance and the toxic chat when I was just trying to explain what happened - I even posted a topic on it, it unsettled me so much - and I'm out.
I wish the game could see the disparity between certain encounters and respond accordingly. An experienced, high-ranked player in a well-engineered armed ship being interdicted and attacked while wanted and carrying high-value cargo is the exact opposite end of the chart vs. the relatively new, clean, low-ranked player in the unengineered E-Rated ship they just bought carrying no cargo. The range of PvP interaction is wide, the game should recognise this when it comes to responding to hostilities. In the former example, obviously the attacked player is the "Bad guy" wanted Pirate, whereas the attacker is the "good guy" bounty hunter. In the later the attacker is quite simply a ganker, or "seal clubber" (unsavoury term) as some like to call them. There is little gameplay for the totally out-class victim. In high security systems, their should be better protection and response to hostilities.
Regarding Open PvP in general. I have good combat ships available and have been fairly competent at combat in the past - a bit rusty at the moment - however, the last thing I'd want is to think I'd ruined the evening of someone I don't know by choosing to destroy their ship for my own lolz if there's no valid gameplay reason. I've NEVER destroyed another player's ship, however, "valid" reasons might be: Opposing faction in CZ, they're a wanted Pirate in a Res site, they're a valid Piracy target or an assassination target. Never done any of those and, indeed, I've left an instance where a Player was on the other side of a CZ and where a "Wanted" player was flying around a Res Site. I just didn't want that interaction at the time as I prefer co-op activities.
Anyway, that's my ramble on the topic, performance issues - which I assume are directly linked to network / PC performance - were the thing that finally put me off Open though. I'll have a peaceful evening in group doing my own thing, or team up with freinds for some co-op activities. This is likely how I'll play going forward.