-Five difficulty modes: Normal, Expert, Master, Megaton, Megaton II, unlock through story. All repeatable missions can be cleared in each, giving "First Clear" rewards to incentivize playing every mission on every difficulty at least once.
-Main story seems to be roughly 25-30 hours if done in a straight line. Side content, however, is several hundred hours across multiple game modes including PVE, PVP, a Roguelike mode, clear a mission once and you can see the loot table for maximum farming efficiency.
-The sex scene was cut from the game, and is anime only. Why it was included in the first place, I'll never know, but it actually is surprisingly relevant to the overall story with a thinly veiled "post-birth abortion vs stem cell research debate" sub-plot. No, I'm not joking, I wish I were!
-If you're wondering how to unlock [X], when in doubt, progress through the story. Clear a story mission, things are likely to unlock - side missions unlock areas and functions as well.
-Combat is an arcade-style ARPG beat-em-up on ground and air, unlock combos and weapon skills through the Motherboard development system. You can go very fast, but so do your enemies, auto-target is your best friend until you get used to the speed to minimize mistakes. There are bonuses for manual aiming and precise evasion, as an example of what a skilled player could possibly accomplish.
-Level up + enhance + mod your equipment, progress through the Motherboard development tech tree with loot drops. Allocate skill points to each pilot, increase your overall power for every mech in your team. Elemental + damage attributes with RNG modifier rolls and color-tier rarity on each piece of equipment (though only weapons have elemental and damage attributes), and each piece of equipment/mecha can have different paint jobs. Collect one of each color tier rarity and maximum enhancement to unlock permanent stat bonuses for all of the mechs in your team. Lots of these equipment and mods can be crafted as well, utilizing loot drops and recycled materials, to help speed up the perfect-roll grind. Unironically, a better ARPG build and loot game than Diablo IV.
-Progress in PVE and PVP is separate, so that you don't bring over your tricked out build in competitive, and all equipment is equalized in level with its own motherboard to progress. They also have different loot inventories, so grind the PVP mode to get PVP gear, because the developers understand that people will want to make overpowered builds to fight against superbosses in PVE, without ruining the balance of PVP.
-PVP is very much like Mario Kart with its item spawns: tug-of-war arena based team deathmatch where you break boxes that could have randomized skills and team benefits, so it's entirely possible to nuke the opposing team when they're seconds away from victory.
-If you want to unlock [X] feature in PVP, play the story! Seriously, play through the story, things will constantly unlock, and the Japanese players are already years ahead of you so get any advantage you can!
-Why play PVP or the Roguelike mode? Because there are exclusive Mecha sets to those modes - same with co-op, where you get currency that you can spend on a treasure box with a chance for a part in the co-op exclusive set. The developers really made sure that there is always a reason to play the content they make for the game, even if it is just filling up your collection or getting the best stats on a mode-exclusive set piece.
-You also unlock things through achievements, and you get achievements by clearing most content in the game. It's a constant stream of rewards that gives resources, equipment, decals, various customization and progression based rewards to incentivize doing activities you normally wouldn't on a casual playthrough.
-Everything about the game is anime, and that seems to be a filter for some people who just want to skip the story and get to mowing down enemies with mechs. Hot-blooded Shonen protagonists falls in love with Alien Princess while his childhood friend remains forever in the cuck chair. Daily life at school, in the city, and on the battlefield. Mecha choreography and battlefield drama. Misunderstandings rampant, over-reactions, so on and so forth. Guys will look at this and say "hell yeah".
-If you enjoy anime, especially Super Robot Anime, you are going to love this game. Tourists will be otherwise filtered, especially with the stereotypical flamboyant man who is a regular part of Command HQ and constantly flirts with everyone, and the multiple scenes where the joke is "these boys must cross-dress to infiltrate a location and are made fun of by squad members". In fact, you know this game is going under the radar because game journalists aren't making a stink about it yet.