Enjoyable enough if you just want something breezy to put on the background on Christmas, but like most of Moffat's run it's nonsense buoyed by the presence of talented actors and capped off with unearned sentimentality.
Which is not to say the closing scene was bad given that it had Peter and Alex acting the hell out of it, but it might have been more effective if it had dialed back on the "OH NOEZ IT'S THEIR LAST NIGHT TOGETHER BE SAD NOW ISN'T IT POIGNANT" and let the natural tragedy of River not knowing she's about to die speak for itself.
Which is not to say the closing scene was bad given that it had Peter and Alex acting the hell out of it, but it might have been more effective if it had dialed back on the "OH NOEZ IT'S THEIR LAST NIGHT TOGETHER BE SAD NOW ISN'T IT POIGNANT" and let the natural tragedy of River not knowing she's about to die speak for itself.