A mixed bag for me.
The good: decent enough setup, mystery was interesting. Sad to see Clara go (I know many of you weren't fond of her), but it was at least done quickly rather than really stretching it out. Also the foreshadowing across the series with Clara slowly becoming more reckless and doctor-ish, all nearly wrapped up with her being hoist by her own petard.
However - and I realise this comes down to plot armour etc - it seemed such a technicality to go out on. The sort of scrape the doctor always has an answer for, only this time it is absolute. I think that's a failing of just how un-absolute things are in the Who universe. Maisy seems happy to remove the chronolock(?) from the earlier person, yet suddenly there is a gotcha in the small print? That just fell flat to me.
It's the kind of thing the Doctor can get himself out of after getting himself in it. But Clara got herself in this.