When I write my reviews for this site, I don't include numerical marks of any kind. I don't give something 4 stars or something else a score of 9 out of 10. However, when I post links to my reviews on other sites that include such markings, I will often grudgingly apply one. But the truth is, I prefer not to give marks, so that's why you don't see them in the reviews themselves.
This is for a couple simple reasons. Primarily, it's because I find that a simple number doesn't really tell a lot. There's far more nuance to anything than a single score could ever provide. Not only that, different people assign different meanings to scores. One just has to look at the various review threads on Gallifrey Base to see this. One person can call a particular episode terrible and still give it a score of 6 out of 10, while the next person will offer all kinds of praise and give exactly the same score.
But even if everyone were to agree on how good any particular score is, there's still a lot not conveyed by it. If “5 out of 10” means mediocre, does it mean that the whole thing is mediocre or that it's mostly really good but let down by some major part being poor? Perhaps it's the reverse of that, mostly bad but with a major redeeming feature? Or is it all over the place and just sort of averages out to 5? Since all these things need to be explained anyway, I feel it's just better to go ahead and explain them and not worry about assigning a number to go with them.
I've often commented that Steven Moffat's Doctor Who stories can be a mix of brilliance and annoyance, and “The Husbands of River Song” is a definite example of this, and one for which a numerical score would definitely not convey any indication of how good or bad it is. It's definitely an entertaining episode, which is ultimately its main objective and thus is a success. It has some funny moments, some touching moments, and great performances from its two leads. But it also has some terribly unfunny jokes, a paper-thin plot, poor characterisation, and some rather poor performances from several of the guest stars. It also manages to make you both love and hate River Song at the same time—which may, I admit, be intentional. It all makes for a bit of a confounding episode.