Rationalism plays well with Freedom, so choose policies from each. Rationalism has +25% great scientists and Freedom has +25% to all (I think that's right). I haven't done the math to compare if it stacks vs. multiplies but more GS = more free bulbs since you typically don't plant GS after industrial opener (maybe Korea would or if you pick World Congress resolutions that boost landmarks). After that, Rationalism is a lot more situational - wide empires might appreciate gold for science buildings, small ones might not get much from that when there are other policies to take. The finisher is OK if taken late in the game because techs cost huge amounts. I tend to delay Oxford and Rationalism finisher until I need some big techs for a VC (typically dom, sometimes space) and then chain them together to get 2 techs back-to-back. I tend to war a lot so the bonus to research agreements is no help but if you go friendly that can be valuable to.
It definitely is not as overpowered as before, which I think is good. Now it has very specific usages and balances better and I like the synergy with other trees. The only downside is in every, seriously every, BNW game I have played the AIs have never taken policies from it which means I have PT all to myself. That's a shame. Could be sample size, I haven't played against Korea yet in BNW and Neb never does well in my games.