The problem with Tartarus is twofold:
1. Ganging up on one person with 5-10 (exceptionally stupid) allies isn't exactly a very climactic battle.
2. Tartarus is just way too strong to defeat on a 1-on-1.
Maybe it should have been 5-10 Brutes with Tartarus against 5-10 Elites with the Arbiter and Tartarus having a more reasonable shield, like maybe two overcharged shields or something instead of taking all the shots from three sets of twin plasma rifles.. The last fight was a definitely the wrong way to set up a final boss. Compared to the fight against Regret, it felt boring.. And even Regret wasn't exceptional.
Anyway, the last level up until the final boss fight was exceptional, the pacing is great, so I won't complain anymore.