As someone who didn't play the games but watched M-L: Total Eclipse, I can say the latter was an infinitely more enjoyable experience even though both Muv-Luv animes are existing in the same world.
M-L Alt.'s problems come down to 2 major flaws that make it a chore to watch and just generally unpleasant: the pacing and the story is overambitious.
First, like mentioned, the pacing of the story is a major flaw of this anime. At 12 episodes short, M-L A. manages to accomplish nothing of it's initial story which is kind of amazing when you think about it. The premise of the alien invasion (BETAs) is the main plot of the story, yet by the end of this series run nothing of importance towards the resolution of this thread is made. Obviously, any good story needs to take time to establish its world and characters, yet instead of doing these simple things M-L A. just makes its characters spout exposition constantly and goes half-way through every side stories. So much plot points are introduced about every single characters, but barely any story has time to develop or has a continuation/resolution so it just feels like nothing happens for the duration of the series. However, it also feels like some story beats are glossed over. When the series is over it seems like the real main story of this anime went at a breakneck speed and just ended so suddenly.
Which leads directly to the second major flaw of this anime: it's overambitious. What started with a pretty forward story of alien invasion apocalypse (with a twist of parallel universe mumbo-jumbo) ends up with countless divergent stories that don't seem particularly interconnected between each others. The main threat of the series, the BETAs, are never seen again after the first or second episode (except for flashbacks or exposition scenes in no direct contact with the story). In other words, the whole premise of the series has no bearing on this season of M-L A. so anyone interested by this story and liked episode 1 can only be disappointed and feel betrayed by this. No, instead we spend every episode adding more lore about every single thing and person in this anime. Not only do we have the MC's story to follow, his 5 or 6 squad mates individual stories, then professor's story, the head of intelligence story, the royal squad story, the little esper girl's story, the...ahem, well you get the point. What promise to be a kind of mecha/harem/mystery anime ends up being a political wishy-washy nonsensical story about patriotism that is executed with the finesse of a kid playing with a toy. Not only does this sudden turn of story comes half way through the season, it comes from nowhere and none of the stakes and motivations are put forward before this story comes to play. It's just messy and boring from start to finish and feels like this whole ''arc'' was filler and pointless because nothing important happened (or at east it felt that way by the end). We're also introduce to the alternate/parallel universe theory, the history of the five Alternatives, some lore about the BETAs and it just feels overwhelming. Yet at the same time, even though we're catapulted with exposition, somehow it feels like nothing is really explained fully meaning nothing we're told makes sense. M-L A. just doesn't know what it wants to be nor where it wants to go with any of its plot. It's just frustrating and confusing in an increasing pace though its run.
So after all of this, what are we left with? Characters ranging from bland to boring, unimpressive art, unmemorable music, nearly non-existent mecha action that isn't even good and just a overall painstakingly bad viewing experience. M-L A as it stands (a second season has been announced) is not worth your time even at its short runtime of a mere 12 episodes. If you want any semblance of fun from this license, Muv-Luv: Total Eclipse (which is twice has long but definitely twice as better than this anime) is the way to go if you want your mecha vs. aliens fill.
