Like most Gundam games it covers the One Year War. Also like most Gundam games, never released outside of Japan. There's some things that aren't like most Gundam games though...
Firstly there's an actual, full campaign for the good guys of the one year war. ジークジオン!
Second is the tactical layer, where you can order allies around. Has the basic commands you'd expect, but larger vessels have some special commands like bombardments and (most importantly) resupplying allies. Not as well executed as it could be, 75% of stages don't give you any significant number of allies to command limiting you to a pair of wingmen who are only good for clearing cannon fodder and die quickly to named foes. Still, the stages that actually use it make good use of it.
The Zeon campaign opens with the Battle of Loum. It's a fairly easy stage, nuke the bridge of the attacking Salamis ships while manageing your allies to keep the ones in the rest of the mission at bay and finding time to resupply your weapons. I think this is the first time they actually showed the
Battle of Loum, (and other Zeon characters show different versions of this level, most not as easy as Char's) which is interesting.
The game has two main problems that this opening, unfortunately, showcases. 1: The draw distance is horrible, and your radar isn't much better. Somehow this is true in space where the game is barely rendering anything, which makes it even worse. Thanks to a lack of landmarks (it's space) you have to keep checking your tactical layer screen to actually figure out where you're going. 2: The flight is relatively clumsy and completely non-newtonian. The lack of proper space flight physics in any Gundam game (that I'm aware of) is sad given the real physics of flight are why Mobile Suits have limbs in the first place.
That's unfortuate because this game is actually very good about keeping the rules of the original show intact. In the fed campaign one of your biggest problems is how little ammo your weapons have, just as Amuro is forced out of fights repeatedly because he runs out of beam rifle ammo. That's something most Gundam games ignore entirely despite being so critical. A lot of tactics used on the show are also valid in the game: Once the series returned to space Amuro mainly used beam sabers to destroy larger ships, and here it works very well.
All the suits feel quite differently, and the fact that the first leg of the Zeon campaign starts you in the fantasticly weak Zaku II (it has decent burst speed, but can't keep it up without overheating) so you really notice how differently your followup suits handle. After you complete certain Char (or Amuro in the fed campaign) stages you will unlock extra characters (Ramba Ral, the Black TriStars, Bernie ect.) each with their own mission and suits. You can take the "wrong" character or suit to a mission you've already cleared but your rank will only be saved with the "canon" choice.
There's a few other mechanics of note.
The Pressure Gauge is an interesting risk/reward idea: As enemies get too close, attack you (worse if they actually hit) the gauge rises and if it hits max you're fucked untill it recovers, and it lowers as you stay away from the action. To encourage keeping it higher, if it is past certain threshholds (25, 50 and 75) your skills (limited used buffs) get more powerful, but what buffs you can use also changes and each character has his own list of buff options. The pressure has different effects on each characters: Char gets less options in a linear fashinon, with Kai and Amuro the opposite, while Lalah's selection isn't effected at all.
Each pilot also levels up, which earns them better stats (rates depend on pilot) and also new equipable skills. You have 4 categories and can only equip one of each category at a time. Each character gains these at different rates and powers, but most are just buffs to certain abilities (do more damage with this, take less from that) with the exception of the one that lets you aim in first person by pressing up on the d-pad (which is essentially useless, this is a fast game with low draw distance and no mouse controls).
Overall I recommend it, though it could have been betters.
If you know the plot and are filling to learn the menus it's playable without 日本語 knowledge.