It was a solid set, with nice graphics.
The "weakness" was that it was resistance-based, and for much of the game, it was a lot easier to stack Defense buffs and To Hit Debuffs to floor the enemy's chance to hit, than it was to stack Resistance buffs to reach the Resistance caps. Now, if you're already working with teammates that have some resists to begin with (or a Controller with a pet that has nice Resists such as Gravity or Earth), and you could get them to the caps or near them, it was very strong defensively. But it was more likely that you'd get onto a team with a Defense/-ToHit based set such as Empathy or Dark Affinity, and help them cap out there, than it was that you'd get onto a team with solid base Resistance, or with another Resist buffer, and cap out the Resists.
So its main problem wasn't inherent to the set but just due to the fact that it's better to stack the same kind of mitigation until you're at the cap, and that it was easier to find sources of Defense than of Resistance.
But for some sets that have good Resists already, it was a great secondary... Earth Control, Gravity Control, Demon Summoning, Beast Mastery.