A notorious Zerg complaint has been lack of viable scouting options and being reduced to guessing what the opponent is doing. More so than Protoss and Terran, Zerg has very limited options and specific responses to many Protoss and Terran builds which will kill the Zerg player outright if the Zerg doesn't have ample preparation time.
The problem with that is that those builds which will kill the Zerg player all hit before Zerg has access to better scouting methods. While it's true that Protoss also suffers from poor scouting before hallucination or robotics tech, Protoss walks less of a razor's edge leading into the mid-game and has more "catch all" builds that leave the Protoss player capable of responding to most threats.
As far as Zerg goes, the biggest "I need to scout" threats are 4gate, void rays, banshees, and marine/scv all-ins. Less common rushes such as Dark Templar are also possible. In addition, many "normal" Terran builds can kill the Zerg player that isn't properly prepared, even the somewhat silly mass-hellion. Failing to scout one of the above builds with plenty of time to prepare is GG for the Zerg player.
Zerg has 2 methods for scouting in the early game: Overlords and checking the front. In the past, this has been effective on most maps and in most circumstances. However, it has still been possible for a player to deny both methods of scouting by means of hiding tech and revealing units from the front and keeping marines or stalkers patrolling around the base to shoot down overlords. This problem is exaggerated on large maps.
On many large maps such as Typhon Peaks it is impossible to guarantee yourself a chance at scouting with an overlord. With 3 possible bases to scout there is no way to know where you will need an overlord to be, since the distance is too far to have an overlord at all three (or even 2). Cross spots in particular are a problem, since even your first overlord can't cross the entire map before a marine could be out to shoot it down.
Good luck getting an overlord in my base!
Zerg is left with scouting the front of the base. Unfortunately, the game is such that it is not difficult to hide information from the Zerg player, and it is just as easy to outright deceive them.
Cross position on Typhon Peaks, ZvP. Your zergling has scouted a zealot and stalker at the front, and warpgate tech is being chronoboosted at the cybernetics core. It looks like a 4gate or otherwise early pressure, and you switch into heavy ling/roach production. A few minutes later, after realizing it's too late for the 4gate, the void rays fly into your base and it's GG.
With builds that kill outright, there is the luxury that "smoothness" and refinement of the build can be sacrificed in the name of deception. Although the Protoss player has used his chronoboost and 50 gas on tech that he has no intention of using, it is a meaningless sacrifice given the decisiveness of void rays that have not been prepared against.
In the above example, the Zerg player will die to the 4gate if he chooses to drone much higher than 21 or 22 drones. It is a guessing game. If he loses to the 4gate, he is a fool for having not prepared. If he loses to the void rays, he is justified, but no better off in the end.
Terran, with faster anti-air, can be even harder to scout given the ease of hiding their buildings. Should a Terran player wall off, keep a couple marines patrolling his base, and hide an additional 2 barracks and marines in the furthest corner of their base, there is no way to be sure you can scout it. Even if you have an overlord at their base, there is a strong likelyhood that it will be shot down before it sees what it needs to see.
Basically, I feel like without viable scouting in the early game, Zerg is doomed to a complete guessing game on 4 player maps with large rush distances a significant percentage of the time. What could fix it? Perhaps having overlord speed moved to Spawning Pool tech.
In the immortal words of Idra, "No amount of creativity will get a zergling past a wall or an overlord past a marine."
Do other Zergs feel blind on large maps?