David Weber, Out of the Dark.
The book has an excellent premise: an alien invasion by technologically superior forces where not even asymmetrical warfare (guerrilla warfare) works. Humanity was getting it’s arrogant arse kicked all over the planet.
I guess David realized he bit off more than he could chew, because the premise was working itself into a multi-book series. So about halfway through that book he employed a Deus ex Machina by pulling the most perfect opponent to the alien invasion out of his arse: vampires.
Yes, vampires. a force that so perfectly neutralized all of the alien’s advantages that the second half of the book amounts to teenage revenge wish fulfilment as the vampires steamroll the aliens back into orbit - and then eliminate them in orbit - by riding on the outside of their escaping shuttles. Because vampires don’t need to breathe.
I got so disgusted at the lame-arse way of avoiding a truly great story that I nearly threw the book across the room. I forced myself to finish the book to see if it got any better. Spoiler alert: it didn’t.
And now, a decade-plus later, he’s released two sequel books.
smh facepalm bridgepinch sigh