Favourites:
- Ragnarok Online (RO)
- Dungeons & Dragon Online (DDO)

Liked but still important:
- Rift
- Tera
- Cabal Online

Dungeons & Dragons Online and Ragnarok Online
- Dungeon Scaling (amount of party members)
- Different difficulties for all dungeons (Solo, Normal, hard, elite etc.) that do not lock dungeons behind a level wall
- The ability to SOLO/DUO dungeons at level (lower exp /drop rewards)- with exp rewards!
- Party size of up to 6 people (12 for raid parties)
- possibility to use mercenaries in dungeons
- Raids that entail more than some trash mobs and boss rooms
- Introduction of traps in dungeons
- Introduce puzzles that actually need brain mass
- DUNGEON RANDOMIZATION
- Class personalization (choose all stats + skills)
- No time limit in dungeons
- Only 3 day raid loot lockout instead of a whole week (more incentive to play raids)
- No loot lock-outs of doom!

Rift and Tera
- Open world invasions
- wardrobe/glamour systems (no class restrictions!)
- Instanced housing (you can basically build the house yourself - bit by bit)
- (again) class customization
- For the love of everything PROPER LOOKING AND MOVING HORSES!
- Nexus - giant invasion at certain times in switching locations, connected to huge boss fights in private instances after
- More possibilities to get currencies for gear (everything you do should give you certain currencies)
- Soft cap on ALL gear currencies (only max the amount you can carry - meaning, remove the 450 hard cap crap)

PvP (taken from all games)
- Actual Wars for certain castles/territories (between guilds) with access to special rewards/dungeons
- Possibilities of PvP channels for people that are into them
- Again, guild wars in optional territories (people need to be able to avoid it if they want)
(Mind you, I am not much into PvP but it CAN enrich a game if done properly)

I doubt they will listen but it is worth a try....