Love:
-Classic-type DMs where you spawn with basic weapons and collect better weapons as you move around the map.
-Unique themes. As in something that isn't just some generic industrial scene or rundown city.
-A gamemode that I haven't seen in popular FPS games. Because they're all overdone.
Hate:
-'Weapon Selection Rooms'
-'Class Selection Rooms'
(both of these are possible to do completely server sided without having the player spawn and use some broke-ass events just so they can get spawnkilled or remain AFK in the spawn room, or even clog up the limited space)
-One-sided TDMs. Seriously, if you notice one team is winning 90+% of the time, even when it's completely different players, fix it.
-Current grapple rope and hookshot. They're just way too useful to be considered fun. Everyone's just flying all over and nothing ever gets done except fall damage. I've balanced the hookshot before. I found it useful and people kept complaining how they can't just fly all over the map with it.
-Multiple weapons from several different themes/packs. They do not balance well at all. Default guns will always beat tier tactical guns, and people usually price the defaults at a lower cost. Some weapon packs are more powerful than other weapon packs, making the other weapon packs not even used, causing them to just take up space. And when they do get used, the user will just complain that the other weapons are overpowered.
-Vehicles. They seriously just don't work right now. Anything that isn't a wheeledvehicle or a flyingvehicle (aka AiPlayer) ends up being unusable or unfair. (horses move fast and have lots of health)
-Rules. If you need to have a rules board before you spawn in a PvP orientated server, and a constant team of competent admins present at all times, or a vote kick system... Consider revising your server. It needs work.