I rated this module more highly for the plotline than playability. It's fun to advance SEER's plotline and even bring her into opposition to characters, particularly for players / characters who have been through much of Season 5.
On the downside, as other reviewers have said, there's so little difficulty that it erodes the enjoyment. When I ran it, the party was Strong-- six PCs and APL 14-- but the only time I made them sweat even a little was using four banshees instead of two (they were still never in serious danger, and none of the banshees survived more than two rounds, but banshees are a good way to make even Tier 3 PCs without Con save proficiency feel nervous). I added an extra Dreamweaver in the first fight, too (and the party had a moment of shock when Greater Restoration didn't immediately work, though they had enough Prayer Beads, Clerics, and Druids that it was a minor setback).
For the final fight, I added a Champion and improved SEER's capabilities a bit (e.g., she had a Globe of Invulnerability). It still wasn't close. I think the boss just doesn't have the damage output to be threatening without significant allies (and for Tier 3, the Charm / Dominate options are unlikely to last very long, possibly not even long enough for the affected PC to act). If I ran it again, I might add two Champions, or maybe a Champion and an Abjurer (and seek to Walls and Banish to split up the PCs). Tactically, it was a fun reversal for the enemies to have more counterspellers than the PCs. Well, it was fun for me and I think an interesting dynamic for the players.
Timewise, it took me about 5.5 hours to run (partly because my monsters tried to play as smartly as they could and partly because there's a lot of not-that-threatening fights). I expected it to be faster because of low difficulty, but it turned out that just chugging through the enemies took some time even though the enemies were largely ineffective during it.
[3 of 5 Stars!]