Good to see you back, Trek Survivor
"Observer Effect" is my favorite ENT episode. The rest of my "top 4" are in Season 3 - "Similitude," "The Forgotton," "Damage."
I also love the Vulcan trilogy because of Soval's character development. It's fun to look at the Soval of earlier seasons in hindsight, knowing the secrets he was keeping - he was a closet melder, he had an affinity for humanity all along, he had a great partnership with Admiral Forrest, and he was basically playing the VHC and serving a higher ideal. I totally loved Soval after this set of episodes. I think he and Archer could have developed a good give-and-take in later seasons, if we'd gotten them, because they finally started to see eye-to-eye in Season 4 and developed a good rapport. Ah, what might have been.
But the loss of Forrest was just...
At least he had a good death, sacrificing himself to save Soval. A good man to the last.