A somewhat related question: Given the above posts, would you recommend the traditional or blended retirement currently being offered this year?
The short answer: It depends. For the overwhelming majority of people, the BRS is a better deal. Something like 87% of servicemembers do not make it to 20 years. Some money > no money.
I think people get wrapped around the axle that:
a: A 50% pension is better than a 40% pension, which is true
b: The Government is doing this, therefore it is ultimately to save money, and therefore a scam that will exploit servicemembers, which is half true (the purpose is to save the government money, but at the end of the day this is, actually, a pretty good deal for most people).
The longer answer: Pretty much everyone in my situation or with under ~8-10 years TIS should probably opt in, with exceptions. Almost everyone on their first enlistment/billet should opt in. Serving to 20 is never a guarantee, especially on the officer side. The military may be hurting for retention now (ex. the Air Force allowing literally anyone to promote to Major), but that can change very quickly. People's personal situations change as well. Single 2ndLt with his hair on fire wanting to fly fighters may be all about staying in for 30 years, eight years down the road that now-Capt with a wife, kids, a couple deployments under his belt ,and the airlines calling may be looking to bounce at his first chance.
I already opted in. I have ~5.5 yrs TIS, am obligated through to 11 years TIS, and am unsure about whether not I am staying in, though leaning towards no. For me it's a no brainer. Even if I decide to stay to 20, I'll have matching on my TSP (to which I contribute much more than the required 5% to get the full match) for 15 years plus my pension. I'll do okay.