I often hear "I want a MMO with Dark Souls combat"... but apparently, everyone is forgetting how amazing the map design is in Dark Souls, and MMO developers should take notes.
In Dark Souls, everything is connected to each other in genuine ways. Hard monsters roam near easy monsters, there is a deep underground level (and upper level), there are a lot mazes, it's slow-pace, etc. And more often than not, you will get lost for a while and then enter a door that suddenly puts you way back at the beginning, mindblowing the hell out of you.
Now, THAT is what exploration is. Usually, MMOs tend to have a huge world that is simply unrealistic. Everything is vast, but there's no depth to anything. Buildings, characters and objects are scaled in a way that you can see everything without having to even explore it. Everything is either too small or too big. Perhaps it's good for big scale PVP, but it's terrible for an actual PVE experience. People say exploring stuff in Guild Wars 2 is awesome, but I thought it was boring as hell. You don't feel like an adventurer, you feel like a tourist being told where to look at on a bus trip.
With a smaller scale map, you can create a much more complex map with a lot more depth. Also, you get to meet more players along your way, creating a real MMO world. Instead of seeing them one mile away, you see them right beside you.