I just finished Enterprise a few minutes ago.
1. The opening theme grew on me, and perhaps that's because they toned it down in later seasons. The Mirror Universe version of it was hilarious.
2. Speaking of the Mirror Universe, those two episodes were some of my favorites from that theme. The actors always seem to be having fun when they do these.
3. I never really liked the Temporal Cold War and it ended on a lame note. If they ever do a Trek series that features temporal operatives they should make an inside joke or something like have a specific World War II division tasked with preventing errant time travelers from trying to help the Nazis win.
4. Season two was perhaps the weakest, but there weren't any episodes that I hated. I just forgot several of them. However, it had some great ones like "Minefield" and "Cogenitor."
5. Season four was my favorite. Yes, it had a fair amount of fan service but all of the episodes that feature the Andorians are strong and it was amusing to see how they explained the origin of human-looking Klingons.
6. The Xindi war was good but they dragged it on a bit too much with filler episodes such as "Hatchery" and "Exile."
7. Yes, the last episode was bad but I still think the finale for TOS was worse. I just hated Dr. Janice Lester so much that I still consider it to be the worst of them all so far. Maybe Discovery will beat it, but I doubt it will.
Overall, I enjoy this series a great deal. I wish it had continued because then we would have probably seen the war with the Romulans. There weren't any episodes that I outright hated but there weren't any that topped some of the episodes I saw in DS9, which is my favorite series. Given a chance, it would have probably surpassed Voyager, which was all over the place in terms of its goals, but we will never know since it was cut short.