Interesting topic. Got a few things I'd like to add.

[color=8493ca][b][H3]The Good[/h3][/b][/color]
To start off with just simply creating some amazing characters and seeing others enjoy my creation. It's nice when a roleplaying partner is willing to team up with your character because they want to explore them more. That little bit is just enough to make you feel like you are a part of the roleplay rather than an NPC. One of my favourite scenes was when another player knocked me off a building because of a parachute incident. It was fun and ended amusingly.

Following on from that I've had a few RPs where similar members have joined and it's nice to set out on a new journey with such members. You know their style and how they work so teaming up is quite the enjoyable task.

[color=8493ca][b][H3]The Bad[/h3][/b][/color]
Here is where the problems start. Most of the RPs I have entered have died. A few are due to GMs leaving and some are due to the drop off in players which have changed the dynamic of the RP. It just gets frustrating when you spent this effort and it all falls to shit. I know it's the nature of roleplaying but there needs to be at least one RP I join that doesn't end for silly reasons.

The next point I'll make is the way some people operate a roleplay. Some of the roleplays have had less than desirable players or GMs. One roleplay I left was due to the players speed posting and what started off as a cool concept, died, because people didn't have the restraint to not manage their post speed (multiple times per day). I don't know of many people that leave for a day due to to life and when they come back there's 2 pages to read up already.

This also comes down to the GM and their ability on when to manage the members or the story. So often I'll see a GM that doesn't know what they are doing, or runs the RP like a player. Starting a story with 1 character perspective doesn't always lay the scene for the others to enter, unnecessary time skips don't give people the opportunity to complete their interactions, and holding back the mystery can often leave people confused and uncertain with what to do. I'm not saying every secret in a roleplay should be explored and explained, but not being clear about it can risk having a player undermine that secret if they do something unexpected... which they will.

[color=8493ca][b][H3]The Ugly[/h3][/b][/color]
People...
Some of the worse things I have seen are just the people in a roleplay who have single handily ruined a roleplay. I've seen GMs swear at other members, I've seen people powerplay, metagame, godmod their characters and get all snarky when they are told that what they did was wrong, I have even seen someone in an OOC chat ask invasive sexual questions to a minor.

If I could have a roleplay that I enter where it lasts a while with no, or at most, a few minor problems... fine... but there always seems to be one arrogant asshole who has the sole desire of single handily ruin a roleplay.