Interaction with the Navy is a big one (routine inter-service rivalry, no unified command, no Navy man in charge and on-site committed to making McClellan's plan work).
Hard to blame McClellan for that one as he'd been promised support by the Navy (Fox promised it, but it was qualified as "for landing 1st Corps" and not for anything else explicitly).
Interaction with the administration is another (McClellan had not really gotten the President/Stanton/the War Department involved enough, committed enough, informed enough -- which leads directly to a bunch of other issues).
While arguably true, you have to ask how he could have done much better on this aspect - given he was also planning and implementing a war strategy himself. There's only so much time to do things in, and we've already seen that McClellan was being promised things by the administration they either could not or would not provide (i.e. naval support).
If someone promises support, then that's usually taken to mean they're on board... but it's actually worse than this, as all of McClellan's planning had been towards Urbanna. McClellan definitively committed to this in mid March, and then Stanton insisted it be put to a vote of the corps commanders (who, it so happens, were the four who'd decided against Urbanna during the vote of the
division commanders on the 8th of March - their promotions all activated on or about the 13th). They of course came down against the Urbanna movement, and McClellan was required to go for the fallback of the Monroe option - thus there was relatively little planning done towards the Monroe option because it was
not the primary plan.
This was a big problem because Shields had estimated it would take six weeks to get past Yorktown (back in January).
Lack of intelligence on the target area is a major problem -- and since McClellan is the intelligence chief, he can't avoid the responsibility for that.
This is an odd argument, to be honest (especially when taken in conjunction with the above). Either the buck stops with the person who screwed up or it stops with the person with the highest responsibility, surely - but here, in your cases (2) and (3) (and possibly in (1)) you seem to assume the buck stops with McClellan. You blame him for his superiors misunderstanding a military situation and you also blame him for an action that is essentially that of his subordinate (Wool, who provided the maps of the Yorktown area) - though Wool insisted he was an independent commander not under McClellan and Washington confirmed this.
As it happens, the maps showed the Warwick was normally 2 feet deep and 15 feet wide above Lee's Mill (but downstream from Lee's Mill formed a hollow 400 ft wide with 40 ft bluffs on either side). The dams made it 5 feet deep at the fords and 50 feet wide, with Magruder
reporting that "passage is impracticable for either artillery or infantry".
The last time a spy was present at Yorktown (26-28 Jan) he stayed somewhere he should have seen the dams if they were present, but did not report it - so the situation had changed over the last two months.
Also, the Prince de Joinville was the intel chief.
Right there, around March 31- April 4, McClellan's plan is unraveling. Much of that could have been avoided by better work ahead of time.
With clairvoyance, yes. In many cases McClellan hasn't avoided doing the work, he's done the work and the information he's had is actively misleading:
(1) Naval cooperation.
McClellan has been assured of naval support, which turned out to be a promise the Administration could not keep. The
(2) Buy in by Lincoln etc.
McClellan got their approval in person, and specifically planned a phased movement to the Peninsula so as to avoid leaving Washington vulnerable too early in the campaign (including accepting a modification, the removal of Blenker's division, to provide further security for the capital). Almost as soon as he left, however, his GiC appointment was suspended and his papers taken - and his plan of campaign crippled, with the important 1st Corps removed
simply because it was larger. (This also released the Navy from their promise to help, not that they'd done much of that before it happened.)
If someone's told you directly that
no more troops will be removed from your army, then that's generally considered sufficient - instead McClellan had another huge chunk of his army stripped away as a direct violation of that promise. McClellan should presumably not assume the POTUS is going to lie to his face, and either Lincoln was lying or he changed his mind after McClellan left - and in the latter case there's not really much McClellan can do.
Now, maybe McClellan should have taken the Urbanna option, but as we've seen there was some considerable effort by Stanton to sabotage that option (rigging the vote of the commanders as to which option should be taken) and he was forced to fall back on his Monroe option which had only ever been a much later choice. In this light it seems as though the only option Lincoln would be willing to actually accept is the Overland option, but that's both much bloodier (as we saw historically) and something Lincoln was never willing to
order - he just picked away at plans he didn't like, without ever accepting responsibility.
All signs indicate that if Lincoln had given McClellan an order to follow the Overland then McClellan would have followed it - but he would have respectfully disagreed...
(3) Intelligence.
If McClellan had not bothered to procure maps, that would be one thing - but McClellan did secure maps from the local commander (i.e. Wool) so he did take action on this front. Worse, if the maps procured by Wool and whatever additional maps he could have obtained by intelligence (presumably old ones, as one doubts the possibility of landing survey teams on the Peninsula in the middle of a war) had a discrepancy, the sensible thing to do would be to assume the locally obtained maps were correct.
As it happens, there's a map from the LoC which purports to be from 1861 and produced in NY, and it does show the Peninsula - but it shows Yorktown as isolated and the Warwick river as reaching barely halfway across the Peninsula. If McClellan used this map he'd assume there were four and a half miles of open terrain between Yorktown and the Warwick - easily enough to fight an open field battle, even against 20,000 effectives. The maps McClellan actually got were more detailed, but were for January - and showed no sign of the considerable flooding and dam building work.