I recommend it, but it's a definite time investment. I'll give a quick reading guide though since the naming scheme is a bit convoluted. Steam release is the all-ages versions, which is only really relevant if you have a very specific fetish and
possibly has lore implications for NG+ in Unlimited.
- Muv-Luv Extra: Complete Sumika and Meiya's routes to unlock Unlimited. These routes have significant overlap with one another so the second playthrough will be faster if you skip through text you've already read, like Tsukihime's "Near Side". Completing the other heroines' routes (or getting the two 'bad endings' centered on Marimo and Mikoto) isn't necessary, but will fill you in on some background information and explore their characters a bit more. These "far side" routes are about 2/3 as long as the "Near Side", and you get to skip lacrosse, which is a huge plus.
- Any Unlimited route is fine. On NG+ there's a lore-revealing h-scene with Yuuko-sensei but I don't know if that's in the all-ages version.
- Muv-Luv Alternative is the sequel to Extra/Unlimited. This one has no routes, but your choices change which scenes you see in some instances.
- Altered Fable/"Before the Shimmering Time Ends" is a denouement to Alternative set in an altered version of Extra (thus the name). It's to Alternative what FLCL was to End of Evangelion.
From here, you have options: Total Eclipse is set during and after Alternative (it has an anime adaption which is fairly solid, although it ends before the last few chapters of the novel were released on various fandiscs; the Steam version collates them all and includes some cool stuff like using anime footage for animations), and is kind of like Top Gun with giant robots.
The Day After is set in Unlimited, after the events of Unlimited. I'd recommend reading this after Alternative and Total Eclipse, because some stuff happens in TDA that will make more sense with the context of Alt and TE (it's fine even without it, though).
Finally, there are a series of shorter stories that are set in the Unlimited and Alternative timelines, most of which are in collections on Steam now (photonmelodies, photonflowers, etc.). Sadly none of the Steam releases include Faraway Dawn or its sequel, a very challenging and very fun tacRPG set in Alternative. Schwarzesmaken, which is set before the divergence point between Unlimited and Alternative and is more of a WW2/Cold War spy movie aesthetic, also got a 12-episode anime (which has been fansubbed) which has a fabulous soundtrack:
While it's not hugely important to enjoying Muv-Luv (I haven't read them), Extra takes place in the same world as previous ages works (ages is the studio), so characters from that show up every now and then.
There's also a very in-depth series bible, the Codex, which I sadly can't attach to this post, but you shouldn't go anywhere near it until you're finished reading since it casually spoils everything. However, the information, especially the interviews with staff, is
very interesting.
I've uploaded it on my MEGA for anyone who wants it, since I can't remember where I got it from.
I don't know if the all-ages version nerfed it, but in Alternative original, it could get pretty gory when people died, since a huge part of the aesthetic is understanding that you're not going to have a pleasant death in this setting but maybe needing to make a sacrifice for the greater good (the greater good), so you might want to double-check that before you get started if you have a weak stomach.
For me, this (Extra-Unlimited-Alternative) is probably the single greatest work of fiction I've ever read and I am not a shallow reader. I'd say for sure that if you're planning to just sit down and knock them out, you'll probably end up pretty emotionally exhausted. I finished the back half of Alternative over about 18 hours and was just emotionally empty for the next week.
Bad take, Takeru's romcom home is the whole reason Alternative, and to a lesser extent Unlimited, work - they're the core of his motivation, and the contrast between his lives is what drives his development as a character. (Reading Extra and Unlimited is not optional, Alternative trusts that you read them and plot threads that it picks up have been seeded as early as Extra.)
