Its hard to compare seasons 1-3 with 4-5. The first 3 took their time because they had more episodes. One of the things I loved about those seasons is that not everything was SO serious. I think most would agree that "Trisha Tanaka" was a filler episode as far as mythology and plot developement go, but its still my favorite episode and I miss ones like that. Here's mine and lets here yours...
3- Love everything about this season (except Expose). Plenty of action, mythology and laughs. The finale sealed the deal for me.
2- Grew to love it after I realized all the implications it would have and all the mythology tucked away from the first viewing
1- Great backstories and plots for the typical "stranded on an island" concept. Can't believe I used to hate Sawyer
4- Seemed too fasted paced with not much accomplished and was really a transition season. To me, Ben carried this season on his back.
5- Honestly, I hated the time travel thing until the finale and I wasn't interested in the DI. The whole season felt like a chore so some things could be wrapped up. Still the finale was amazing and I'm sure I'll see it in a different light once I watch it again.