The first season, and maybe the second, are absolutely amazing. The last few got really crazy with The Company storyline, from what I remember. I was way into it when it first aired, but thinking back on it now, the last few seasons really don't stand up to the first one.
I'm enjoying the new season for what it is - it's nice to see Lincoln and Michael back in the thick of things. We need more T-bag though. He's been absent for way too many weeks in a row now.