In the Ardennes there is a single mountaineer unit that caused me quite a headache, because I could not move through thick forests.
Is thick forest (i.e forest that cannot be passed at all, forcing you to move a single file along roads) a new concept in PC or was it already in PG? I cannot quite remember at the moment.
Not in the original PG. You can move into the forest, but it is a sloooow progress as you only move one hex per turn. And that INF in there is a pain to deal with, it hits hard. Remember to have one hex free behind your front unit as it will not retreat into the forest, so any retreat result becomes surrender...