I can't really review the game, since I'm not very high level and haven't gotten far, but I'll try to run down the game as much as possible.
I unfortunately can't comment on any story. It's entirely Korean, and I can't read Korean haha.
The game has 2 different types of play, Mission and PvP.
In Mission, you can choose between co-op or solo. It's usually just kill X amount or defend an object etc. Nothing very time-consuming. You are rewarded EXP and Points (in-game currency) as well items once in a while.
PvP, self-explanatory. There are different modes though, like DM, TDM, Boss. I haven't really experimented much with this side honestly, because I'm such low level with low-level Gundams and I get wiped on the floor by everyone else.
There's also a tag-team kind of PvP called "Battleship". You buy battleships with in-game currency, and then you can load it up with Gundams. Higher ranking Gundams, weigh more, and reduce your capacity in the ship. You then fight your opponent and just rotate between your selected Gundams. All of these award EXP and Points.
So this is the part we all are excited for. You know you've always wanted your own Gundam, and here you can have it. There are about 400-500 Gundams in the game, spanning across all of the Gundam series (G-Gundam, Gundam Wing, Seed, etc.) The game is surprisingly balanced while including all of these Gundams.
Gundams, are ranked from C to SS, C being the lowest and most common, while SS being the rarest obviously. There are intermediate ranks like SR or AR, but I'm not entirely sure what they are, probably just different builds. Unfortunately, you can't choose what weapons your Gundam carries; you have to use what the Gundam has. That's probably the balancing factor.
Pilots and Gundams level up alike. Pilots generally serve no purpose, except some Cash ones (IRL currency for virtual items) may give you some sort of in-combat boost. Your ranking allows you to take certain quests though, but that's about it. Gundams level up and acquire their abilities. They're all passive, but are fitted towards maximizing your Gundam's potential. You also get attribute points that you can allocate to your liking between Speed, HP, Agility, Strength, Defense, Special Attack. After leveling up a certain amount of times, you can go "Over Custom", where you level up to 7 times more. You get more attribute points, and if you ever reach EX, you can get an extra EX ability. However, every time you Over Custom one level, you risk losing all Over Custom levels you've gained so far.
To get more Gundams, you can spend Points on a Gachapon machine and get a random one out of the set (They're organized in sets of 6, usually with 4 C's, 1 B, and 1 A, you can pay premium for high ranked sets though). There is also a Custom Gachapon that has EVERY single Gundam, but chances are pretty low anyways. You could also pay with Cash to RENT them for a certain amount of time. Some quests give Gundams, but only at the lower levels to help newbies get somewhere. Finally the last way is Mix-Plans. It's basically a blueprint to create a Gundam. You'll need to acquire the Gundams required by the Mix-Plan, level it up to the required level, then you can activate the Mix-Plan. It's a LOT of work, but that sweet God Gundam at the end makes you look pretty badass. You can have 24 Gundams, but that can be extended with Cash.
So Gundam fans, go ahead and check it out if you have no qualms about the language barrier. I play on the Korean server because my friend had a Korean SSN to register for me, but from what I've read most US people play on Taiwanese servers and are in high populations there.
Cheers and Happy Gaming!
Resources to get you started if you're interested: