Muvluv is the quintessential "no really, it gets good later!" piece of media. But then again, I never understood what people saw in Homestuck.
Muv luv requires you to play through two romances routes that are incredibly boring, has a cast of incredibly flat characters, and writing that has an awful sense of humor.
That lets you unlock the secret storypath in which you train to be a mecha fighter pilot in an alternative timeline where Earth is invaded by aliens. Think "Edge of Tomorrow," in fact, it may be possible that the light novel it was based on "All You Need is Kill" is a bit of a pale imitation of Muv Luv. Except, they edge the hell out of you and you finish the secret storypath without ever fighting or even seeing the aliens you've been training to fight.
Then finally in Muv Luv Alternative, you get the payoff for suffering through hours of setup. Even parts of the very boring romance section suddenly fit in retrospect. The middle parts of Muv Luv Alternative are more immersive than any other media I've read or watched. There's a reason why Muv Luv had an insane amount of backing on Kickstarter, the core parts of Muv Luv Alternative is just absurdly well executed.
It definitely has a lot of flaws, especially towards the end. But man, I easily have it as my favorite visual novel ever despite them. It's hard to recommend due to a huge barrier of entry but its pretty amazing to what lengths the story goes to set up the payoff later on.