There is a hub town, where you can visit 'Works' (it's basically a hangar for your UNITRON), the 'Shop', the 'Arena' where most of the story progression takes place, the 'Square' where you can meet and talk to various NPCs (Non-Player Characters), and the 'W. Map' where you find the various dungeons.  The game makes you talk to all of the NPCs before you start, and I would suggest that after every Arena battle where you gain a rank, that you also talk to all NPCs again, as their text changes, and also you get to know them a bit.  If that wasn't enough, there are a couple of things to miss - one character will train you a couple of times throughout the story, and another will often find rare materials that you can purchase for use in your crafting.

Every UNITRON has a set of base stats: HP for health points, EP for energy points, AP for attack power, SP for defense, RP for accuracy, and MP for movement.  Everything in the game also has an affinity to one of eight affinities.  These include Fire, Wind, Wood, Water, Earth, Light, and Dark.  There is also the rare Mirror affinity that sets yours to be the same as your opponent.  There is a very simple rock/paper/scissors effect with affinities, with the Light/Dark/Mirror ones breaking the pattern a bit.  Light has no weaknesses or strengths (you could argue Mirror is similar), while Dark is strong against anything except for Light, which it's very weak to.  Damage dealt to opponents is highly modified by affinity, as is the damage done to you, so matching up your gear to your opponents is very important.

When you go to the W. Map (from here on out, I'll call it the world map), you can choose from one of four semi-randomly generated dungeons.  Each has an affinity/element, so it's important for you to choose a starting area wisely based on the affinity of your race and weapons.  It's also important to refer to the help documents that show what is strong against what so that you can choose wisely.  Humans are of the Fire affinity, which is strong against Wood, so starting there is advised if you choose to be a human.  Other races are one of the other affinities.  (From what I can tell, the Mariner race has a disadvantage, as there is no dungeon with Fire affinity at the beginning of the game, which it's strong against.)  

Like with many RPGs, most of your powering up will be in these dungeons.  As you fight enemies and gain experience, you will gain levels that increases your 'control' stat; I'm honestly not sure what it does, but you do seem to get a bit more powerful.  The dungeons themselves are semi-randomly generated; they have a pattern, or type, but the exact layout can change each time you visit.  Each one is seven levels deep, and each gets progressively more challenging until level seven, which has a massive difficulty spike.  The good news is that once you're able to complete your first dungeon, things get progressively easier because you can just swap equipment (and elements, as you can set it via an accessory) and go to town on the new enemies.  There is a nice reward if you are able to clear a dungeon, in both loot found as well as earning a badge.  (These badges don't play much role in the story, and from what I could tell, you can theoretically beat the game without earning them - but it's worth doing so as the loot drops from the bosses are worth it.)

In order to really increase your power level, you need to buy (or find) better armor and accessories, and craft better weapons.  Crafting weapons is probably the biggest area of strategy, as you will be figuring out ways to combine your existing or purchased weapons along with various materials to upgrade them.  Depending on what material is used, you may get a different result, though one type of weapon does have a limited number of upgrade options.  The tech tree is honestly not all that complicated on the whole, and most of it can be figured out with a fair amount of trial and error.  Speaking of which, all crafting has some chance of failure, and tools exist to help increase the chance of success.  Each time you craft something your partner's level increases, which makes future crafting easier as well.  Regardless, this is a wonderful opportunity for saving and reloading, since losing your precious weapon (and perhaps more importantly material) isn't usually worth it when you can just save and reload on failure.

Battles in BIOMOTOR UNITRON are usually random outside of the Arena, in that after a few steps in a dungeon, the game will visually transition to a battle screen, where you fight against a monster or robot one-on-one.  Each round, whoever has the higher MP stat goes first, and it's a very simple 'I attack, you attack' kind of thing.  It's most similar to Pokemon, except you don't get to switch out.  If you run out of EP in a battle, you can execute the 'Charge' command to get some back.  There are also healing items, though if you run out of those things can get dicey.  All attacks use EP, so managing that resource is already really important.

Arena battles are quite straightforward, with you simply fighting enemies one after another.  If you defeat all of the ones listed for that rank, you earn that rank.  The story also progresses this way (whatever little there is), so be sure to visit the Shop and talk to everyone in the Square.

The graphics and music are pretty decent for the limitations of the Neo Geo Pocket.  I found the sprite work to be of fairly high quality given the super low resolution screen, and the chiptune music to be remarkably catchy.  Nothing groundbreaking, but also quite serviceable; it would even get stuck in my head on occasion.

Morally, there are a few things to note.  One of the female NPCs has an outfit that shows significant cleavage, and a few enemies are even topless (though without enough pixel resolution to really show much).  Some NPCs drink quite regularly, and one is always drunk when you see him.  Enemies include both living mythical creatures like golems and mermen, but also a fair amount of undead skeletons and zombies.  While all special attacks are represented by technology, several are mystical/magical in their effects.  I did not see any foul language of note, nor any sexual content outside of the scantily-clad females mentioned before.

At first, I found the grind in BIOMOTOR UNITRON's random battles and dungeons somewhat tiring, but once I got my groove, and I remembered that this was how it always was with older games and random fights, I came to accept it and appreciate what this game was trying to do.  It is by no means a complex game, nor does it have a lot of modern creature comforts.  Nor is it a long game with much to the story.  But if you want a simple RPG from a simpler era, it certainly fits that bill quite well.  If that describes you, or if you want a taste from an earlier era of RPGs, then I definitely can recommend this game.  If the constant random battles seem like they would frustrate you, and if you are looking for a deep story or world-building in your games, then this probably isn't for you; look elsewhere.