the requirement to land on a specific square to actually get to the very center.
for hours this went on, we eventually just called it 2 people had talismans one was in the middle ring and no matter what just could not land on the door.
Actually, landing directly on the Portal of Power does not let you cross over. You WANT to roll enough to move past it, so that you can move through it. I can understand why this would be confusing, since all of the movement that does not concern crossing regions is effectively a "straight" line in one direction or the other.
When you reach the Sentinel Bridge (or the Portal of Power) you have reached a point where the path branches. You can choose to continue moving in the same region you were already in, ultimately encountering whatever space you land on, OR you can choose to cross the bridge/portal to get into the region on the other side. You must have at least one point of movement remaining in order to cross, and that is when you must deal with the effects of crossing.
If you land exactly in the Sentinel or Portal space, you do not encounter the effects of trying to cross over. Page 18 (of the FFG rulebook) has a very clear example of the Sorceress crossing the Sentinel Bridge in the middle of her movement and continuing through the middle region.
The same is true for moving in/out of the expansion boards. You don't need to land exactly on the Ruins to get into the Dungeon (for example.) If you're moving past the Ruins, you can choose to hang a left and go into the Dungeon with your remaining move.