I'll agree with Knight. Peace. There was no peace in my heart when I struggled with the cocktail of theologies I was confused with growing up. The unspoken rule in my family regarding theology is "Thou Shalt Not Question" and that just wasn't good enough for me, as we attended a few different churches and I was taught some things that conflicted. Church was not a time for worship, but a mandated time to be counted. It felt very synthetic to me, quite actually.
I was introduced to reformed theology a little over a year ago and was angry at this "new" teaching that contradicted nearly everything the concoction of theology I had grown up with. My initial goal from that point was to use the scriptures to refute this teaching, but the loving, accepting, understanding Calvinists answered all of my questions with the one thing I wouldn't deny. Scripture. Since then, I have had several people of other belief systems lash out at me, not for what I said or did but for what I am unashamed to admit that I believe.
There are also examples of reformed people acting as if they are somehow entitled, which flies in the face of this system from its very core. I have used scripture to refute them, and for the most part, that has settled any disagreements. With reformed people, an argument does not have to become a fight, for we understand that God is the one who goes before us.
I was arminian the first time I read the Bible. There were many passages that contradicted my belief system and I couldn't tie the canon together. I no longer skim past the difficult passages, but seek to be reformed through a more inductive understanding of them.
My prayer life is also better, as I pray for God's will in all things, knowing that the answer to each prayer is based not on my temporal wishes, but on the glory and purpose of God. I see prayer as a time of marinating myself in Him, seeking only to take on more of a flavor of God.
Worship is like a set of scales. God is on one side, I am on the other. The higher I place myself, the lower God must be in my heart. Reformed doctrine seeks to correct this imbalanced view with one that humbles me and lifts up God in my heart.
I could go on and on about how liberating it is to be reformed, but I'll yield the podium to the next person.