If I were still a predestinarian Baptist, this might hold some interest for me. I actually have a whole shelf of Piper's books. Like so many from the Baptist fold, his writings helped to stir a fire in my soul for a vision of the sovereign God.
However...
For all the amazing good that John Piper and Bethlehem Baptist Church are doing there are still many grave concerns to be raised. From my reading of his works, Piper's theology is most heavily influenced by a blend of Jonathan Edwards and Daniel Fuller. From my viewpoint, I think this bears some bad fruit, particularly in an overly charismatic bent (a la Edwards) and some alarming Law-Gospel issues at times (a la Fuller). More broadly speaking, Piper is no covenant theologian (at least not in the historic Reformed sense) and he's not about to sign even the 1689 LBC.
If you're a broadly evangelical Baptist who has come to love the doctrines of grace, then it sounds like you should start to put TBI on your radar next to Southern. If you're a "Reformed" Baptist who subscribes the 1689, Piper and TBI will give you a number of headaches on issues such as:
The Sabbath (no sabbatarians there)
The 2nd Commandment (check out Desiring God's children's materials)
The Regulative Principle (Christian rap solos anyone?)
The Apostolic Sign-Gifts (no cessationists there either)
If you're Reformed according to the Reformed confessions, I don't think TBI should be particularly attractive at all. Again, I have great respect for Piper and his ministry. I'm sure that there are more than a few of us who owe a lot to him for starting us on our journey to a Reformed confession. Glory be to God that I didn't stop there.
Take a look at the Reformed seminaries which are faithfully teaching the full counsel of God. We are blessed here in North America to have quite a few to choose from.