My Investigators insisted me that CC is bad-designed, especially too big map, 

because for Objective 1A we played, (Keeper wins with last event card, Investigators win with all escape)

• It takes at least 50 movements to move between gallery-freezer-coat room-tower-library-gallery
• Thus main key carrier should run for 17 turns to discover all the clue, ignoring all the other exploration, solving all the puzzles with one trial.
• CC has 20 turns (3-3-3-5-6)
• Therefore if Keeper stops the carrier for 10 movement it is impossible for key carrier to discover 1A and escape.
• And it can be done really easily with Panic, several mythos cards, Urges, etc.

Is the Objective 1A is originally designed to be disclosed with Event 4? Or my investigators or keeper (me) is doing something wrong?

----

…in addition, they also told me that the basic scenarios are bad-designed because,

• It is impossible for them to guess what the Objective is, without Clue 1. All the other clues tells simply where the next clue is. The only information about what the Objective is "what the Keeper does".
• The key and lock system is too straightforward, making an investigator as a "KEY CARRIER". All the other investigators felt they are doing something useless, because they cannot help the KEY CARRIER to solve the scenario faster. All they can do is cleaning the monsters, finding the locked doors, and if all done, killing time…
• Revealing Objective with Event 4 is a really bad system, because SUDDENLY they must give up all the clue-finding process and follow the winning scenario.
• There are a lot of endings with "all these were planned to fxxx you up", for example, in fact the monsters just wanted your sample, in fact the main host who wanted you is a bad guy, in fact the Mi-Gos just wanted your brain…. etc. (In fact I chose the Objective at random, thus it's all my bad luck)

A player told me he will give up playing MoM if this pattern repeats. boom….

The scenario we haven't played yet is Green-eyed boy. Is is a good one? (scared)

Crap, software ate my reply .

Anyway, nice to see other sadistic (read: normal) Keepers placing the second Clue in the Coat Room (for longest backtrack) . If you want to go soft on your investigators, placing it in the Bathroom takes two turns out of the run cycle.

Why is not being able to guess the Objective a bad thing? Investigators, if they didn't have to look for the Clues, could just sit on the Start space and wait for the Objective to get revealed and if it were an escape one (House Lynch, Inner Sanctum, CC and Green-Eyed Boy all have one IIRC). and leave. Making them have to find the Clues, possibly revealing the Objective before Event IV also helps them as sometimes to win the investigators need Clue 1 (or something that is seeded with it).

For me, GEB is the worst of the base game scenarios, but then, I like CC which is disliked the most by the majority of MoM players. GEB has a very large map as well, my only play of it, investigators weren't anywhere near Clue 1, might actually be they didn't even find Clue 2. But one play of GEB was all I'm willing to do, horrible scenario in my book.

Dam said:

First, thank you for your support. I was also a sadistic (but read as "normal") Keeper.

My investigators told me about this point as

• The basic Clue-finding, Monster-challanging role-playing game suddenly becomes a totally different one when the objective card is revealed. This is somewhat my problem, because I never told them what the three objective is. I'm not sure I should notice them before the scenario, "there are three objectives, one is escaping, one is killing, and one spawns the Shoggy. I'll choose one from these."
• After noticing what the objective is, the game is too short to handle, especially the escaping objective compared to the distance between the Clue 1 and the Starting Point. Keeper can win the game easily if Keeper is holding no-check-one-horror mythos card and Panic Trauma, 

So, they suggested,

• At least, the other Clues should announce a blur approach about the Clue 1. For example, one player suggested an house rule, "the keeper should read aloud the two possible objectives when the Clue 2 is found, real one and fake one." 
• The last event should occur a little bit later for some Objective. That player suggested me an house rule, "If the Objective is revealed with the Event 4, the last event card needs 1 more time counters to be resolved. (at least for the escaping objective plz)". But I'm not sure this rule is good or not, because it gives awards to the Investigators, not Keeper, when Keeper disturbed them really well…

But I had to tell the "I'll consider that" because I don't know the balance…

My players and I play to see the Investigators die lol, so there is no disappointment. With that said, are you Keepers choosing your set up at random using the 1-6 ABC tiles or choosing the set-up yourself? The difference is phenomenal as a Keeper who chose his set-up completely could, as Dam said, make the clue go two extra spaces further in the Coat Room, or plan accordingly to other set-ups that would further an agenda that was planned either before the game or an environment/monster/threat combination that would ensure Investigator defeat.

Lesson: always use your ABC tiles.

Also I think Classroom Curses and Green-Eyed Boy are two of the poorer made maps for Mansions, and it doesn't sound like you own any of the PoDs. All the PoDs with exception to Silver Tablet are very fun. I'd recommend buying one of those.