Ran my party through this recently, it took us 2.5 sessions. Excellant dungeon. Some highlights:

• Party found the secret door behind the first mural and went through the entire dungeon that way, so they came back to the magic square puzzle much later, having already pryed open the secret door which the puzzle opens from behind. They then agonized over the puzzle for half an hour, finally solved it, and the only effect was that the secret door opened the rest of the way. I thought they were going to kill me, lol. I was told to inform Mason Waaler that he should be afraid for his life if they ever met him, it was fantastic.
• They noticed Albrecht admonishing them for robbing the tomb, so they took their looted goods and threatened to destroy them if he didn't give them information. And then they actually followed through.
• Deciding the glowing red tome was probably evil, they decided to destroy it by throwing it into the forcefield. I decided the resulting magical explosion disabled the field, and vaporized the nearest PC. Good times.
• They also freed Sorn from his tomb. That will be fun down the road. Having him play dead was a great idea, they never suspected a thing.

Only thing I would change if you're running is to revamp the random encounter table; if you go through the dungeon like we did there was an entire session with no combat, and most of the random encounters are just visions or noncombatants. The pacing kind of dragged without the threat of violence to stir things up. Add some skeletal guards or the Red Wraith actually showing up. Also, because they came from behind, I didn't realize a couple of the doors were supposed to be locked, but that's a minor point.

Overall 5/5, has everything you could want in a barrow adventure.