The OnePlus One looks very impressive, but I think what makes the Moto G such good value is that, unless you want to play the most powerful games, the performance from Snapdragon 400 is more than ample.
There's no lagging and it's a very smooth experience - precisely what most other devices at that price point usually aren't.
The reason to stump up a bit more for the OnePlus One wouldn't be for a better day to day experience, but for a better screen, camera, or 4G (but it doesn't support 800MHz, so not much use for Vodafone or O2's 4G service, or indeed when EE and Three roll out 800MHz).
It's great to have some good choices now though - and when Motorola launches its next device(s) it seems people on limited budgets, or simply not wanting to pay hundreds for what they see more as a tool, will have lots of options.
I hope this might one day force all of the dross off the market, but sadly I doubt it as some retailers are perfectly happy to import crap for sub-$50 dollars and flog it on at £100 (mostly tablets I am referring to here, mind).