Is it too early to say they should have stopped at Season 3? Judging from this trailer, I'm not too interested. But will give it a shot.
I will watch but it feels like when a band does a farewell tour and hypes it up, drives up demand and pricing, just to return not too long later. All the marketing, and lead up to s3, then the season itself had such a sense of finality to it that I'm finding it hard to get excited for this until I've seen what they've conjured up. It's not like s3 was really in any way open ended, or had detractors who felt like they didn't get adequate closure.
So I guess spoiler warning, Ted decides to stay at the end of season 3 (I'm currently on the season finale of 3 and about halfway through the episode)