Tried it as well. Exp for bosses is about halved, exp for regular mobs is about 2.5x what it was (but they also have higher HP). Regular mobs keep spawning, so you could stay in the same map forever if you wanted to. The maps are not flat, as mentioned above, but most of them are also not interesting. They just go up and down to be annoying. No platforms or anything.
Going through a "Hatch" (NPC) lands you in a dark "underground bunker". Not sure if there is anything special you're supposed to do or find there, I walked around a bit until I found another Hatch and it took me out. I don't recommend going in there without a vertical tele/grapple/highjump skill. Unless you really like dark JQs. (Or some quest is found that requires that area)
Wolves and purple nependeaths are not bosses anymore. But dinosaurs are.
Didn't stay very long because leaving the Frog map landed me in Spinel's Forest :-(
If it's of any significance: I reached the Frog map from the Wolf map. I exited using the same portal I entered from, curious whether it would take me back or to a random map. (This was the first time I didn't exit through the opposite end of the map).
Edit: Went in on another char. Tried going out of a map through the same portal I came in on, it worked (and took me to a random map).
Edit3: Got into the same exact map configuration, and could go back and forth between wolf and frog maps with no problem. So I have no idea where the game was trying to send me when I ended up in Spinel's Forest.
Edit2: Or my memory is shot. Seems going back through the portal you came in on will take you back to the map you came from.
But trying to go back two maps will take you to a random map.
So this prevents you from simply standing on the portal and pressing "Up" until you find the map you're looking for, without making the island significantly less random.
On the plus side, when you go back to a boss map, it respawns. Which makes the hunt for 10 hogs (or for certain boss drops that are needed for other quests, and don't drop 100%) that much easier. No idea whether the exp gained this way is better than staying on a normal mob map (where they respawn).