My wife and I are both feds, so we've become TSP wizards.
I encourage everyone with access to the TSP to take full advantage. The offerings are solid, the expense ratios are fantastic, the administration and communications are first rate, and the withdrawal options are numerous.
The TSP does have a couple of downsides. It doesn't really offer you much in emerging markets, and the Lifecycle funds which automatically rebalance daily (and which I generally recommend for ease of implementation) don't necessarily age out quite the way I would like. Those are quibbles, though, and easily rectified with other investments or by choosing a different L fund.
The Roth TSP option is generally to be avoided by Mustachians unless you're military and have tax-exempt combat pay. It primarily benefits people who will work long careers and oversave for retirement, like politicians and judges. I'd stick with the regular TSP, and thank your lucky stars for it. It's one of the only redeeming perks of being a fed these days.