I’m a single-player kinda guy so I generally don’t really like multiplayer-only games. However, online-only games can also be single-player games with online functionality (think stuff like Hitman or Mirror’s Edge: Catalyst, though I think both of those can also be played offline). In those cases I don’t mind it while playing but I do think it becomes problematic when you think about game preservation. Games which are truly dependant on official servers run the risk of becoming unplayable once the company shuts down those servers (for whatever reason). So yeah, if your game isn’t an outright multiplayer game that needs an online connection to even work in the first place, I think developers should think twice about making their game online-only without the option to have an offline mode. As for multiplayer games, I think it’s always a good idea to allow people to set up their own servers.