I don't mind jRPGs, and I am not ashamed to call myself a genuine fan of some of them : FF6, Chrono Trigger, Valkyrie Profile, Jeanne d'Arc, Legend of Mana, Seiken Densetsu, Sengoku/Kichiku Rance, <insert a rather large list of other games here>, etc. However I didn't like any of FM games that I've played (FM1, FM4, FM5), and I wouldn't consider them as worth playing. Below are the reasons explaining why it is my opinion.
I will only focus on FM5 during my short (and rather unstructured I am afraid) review, since it's being universally touted as the best of the series.
1/ the main protagonist, which is basically you, the player.
He is the epitome of the typical beta male posing as the leader of an elite squadron (of badass mechs/"wanzers"), and he is a disaster. If you've ever wondered what too much emo in a single human being produces, look no further. No offence meant to sissies, but if I wanted to play as a sissy, I would play a game about sissies, not badass mechs. He also has terrible side-kicks (seconds in command), that I sometimes just want to punch in the face, but that's probably just a personal preference.
2/ the story is unconvincing and sometimes just a pathetic excuse for lame cutscenes.
First example : you are close to achieve one of your first missions against one of your enemies, a huge (supposedly indestructible mech) that came to devastate everything on its path. You manage to beat the mech, quite easily I might add, but suddenly another puny mech appears out of nowhere, dashes up to you faster than any mech in the game could ever do, snipes one of your squad buddies, and disappears again, leaving you unable to react (since it's a cutscene).
Second example : you are close to achieve another mission, which has you protecting landing vessels on a beach, so that your troops can return to the safety of the carrier waiting at several miles from the shore. All goes well, you heroically destroy your opponents, but one of them manages to stand up in an ultimate effort to backstab you while you prepare to board the vessels. You are saved because the amiral emo ninja girl that is secretely in love with emo badass squad leader snipes the enemy mech from the deck of the carrier, which, and it's worth repeating, is miles and miles away... with some kind of a WW2 machine gun.
Last example : at this point, you think that there are people with awesome sniping/markmans skills in this game, and the emo ninja girl that "saved" you in the beach mission has to be one of them. The story explains she has hardcore, black belt, special ops training. However, another cutscene comes to contradict that feeling, since it shows her unable to shoot someone standing just a couple of feet away from her, taunting her, before flying away unmolested in a helicopter. The result is that she starts crying, and the main protagonist proceeds to comfort her and hold her longingly in his, uh, not-so-manly embrace.
3/ the gameplay is underwhelming.
Your squadron of mechs is supposed to be an elite one, the best one of the international forces that you are part of. Yet, your mechs will keep missing, and missing, and missing their hits in battle, even against probably under-trained and unprepared civilians "terrorists", even if your current gear is perfectly up to date or even superior to your enemies. I don't mind a couple of misses here and there, especially against stronger opponents, but it infuriates me to no end when it's so recurrent in games and happens even against grunts.
You can upgrade your mechs. To do so, you need money. You'd think that as part of international military forces, you'd have the opportunity to get the best equipment for your mechs, by successfully achieving missions or ranks. Not so in FM5. Regular army troops actually have inferior base equipment to random rogue elements, and so do you. Not only will you have to buy the gear of your mechs with your own money, but to earn that cash you'll have to participate in some idiotic arena games, betting against your fellow soldiers. If you think about it for a moment, this basically means that you are parasiting allied forces to upgrade your own forces. Therefore... let's not think too much. As the story elements above already proved us, FM5 doesn't encourage you to think. Indeed, I should mention that the aforementioned arena games are non-interactive cutscenes, with entirely random outcomes. That is right, during those arena fights, you will watch your mech moving around, shooting, using skills, most of the time in utterly moronic ways, with no way for you to intervene. You will just watch getting rammed in the ass by newbies. Till the last parts of the game, if the RNG decides to let you win those arena matches, you will earn peanuts too. So the question is, how do you upgrade your mechs, if you can't do it in a logical way (through missions), or through random casino games ?
You'll do it through simulator missions. That's right, the army can't offer you a decent pay for regular missions on the battlefield, but they can if you succeed at virtual simulator missions. That makes perfect sense. Doing those simulator missions is a pita. Some of them are of the "survive as a lone wolf in a dungeon of x levels" type. You enter the simulator with basic equipment each time, with all your skills artificially set to level 1, and progress through it till say level 10 of the dungeon, then level 20, etc. You collect real (?) gear on virtual enemies that you beat in the dungeon. At the end of the dungeon, you get to keep only 3, 4 or 5 items though (IIRC). Most of the time, you will not want to sell the stuff you got (since it's better than anything that you can buy or find outside these "virtual" missions), so you're bound to repeat those dungeon missions several times to also collect stuff that you can sell (doubles). Basically, each time you want to upgrade your mechs, you go through ever-increasing levels of a random dungeon with virtual enemies. How fun that is... not.
4/ your squad team mates.
For me, one of the most promising parts of FM5 (compared to FM4, for example) was the fact that you could now recruit new people to your squad. You do so by talking to NPCs before your mission briefings. They will offer to join you if your reputation is high enough. Each NPC has their speciality (gunner, artillery, close combat, etc.), their personality on the battle-field (in a range from caring/support to aggressive/berserker) and their expertise (level). Some of the NPCs even have special "S" (secret) skills, which are supposed to be rare and valuable. Unfortunately, this part of the game is as underwhelming as all the other parts of the game.
Your reputation basically sums up to your current (skill) level. Nothing else matters : neither your courage (successfully achieving higher level missions, for example), nor your tactical skills (keeping all your squad mates alive during missions) seem to matter.
If you don't recruit a NPC whenever the opportunity arises (at level = x), and you level up (x+1), all NPCs to be recruited will keep levelling up by themselves, automatically. This basically means that the optimal time to recruit someone is to wait for the longest time possible, till you really need them, so that you don't have to train them. Unfortunately, this time never arises, since your own team mates will have levelled up with you, and there is no real difference between them and the other NPCs, except maybe in their personality, which to be honest, doesn't matter all that much, and those special "S" skills.
So what's so special about those "S" skills you may wonder ? Nothing much in opinion. If some "S" skills have an obvious benefit, they also come with a drawback : better offence, but less defence, for example. There are special, special NPCs (otherwise said, special "S" NPCs), which might be worth the effort to look out for, but you'll probably need a guide (gamefaqs) to recruit them, or rely on pure luck, since some will disappear if you talk to them more than three times before recruiting them, some others will need to be recruited during the summer equinox at 3PM precisely, not before, not later, etc. (making this up, but you get the drift).
Conclusion
If some of the missions can be really fun and quite challenging to play (the one which has you conquering a base in enemy territory, and then defending it against overwhelming enemy forces, à la "Fort Alamo", comes to my mind), you'll inevitably run into the issues I've mentioned above.
Upgrading your mechs is a chore more than an exercice of analyzing, acquiring and optimizing your assets that it should be. Cutscenes may have been quite a novelty for the time that the game was released at, and maybe explain why some fans of the game seem so adamant to drool over it, but they don't make a story good. It fails to make sense in the worst times, leaving you with a distasteful "why am I playing this again?" taste in your proverbial gamer's mouth, and a :picard: facepalm in front of your screen. Too many elements of the gameplay itself (during battles, but also outside) rely on random outcomes that the decisions of the player have no impact on, which I consider to be a serious handicap to the value of a game that sells itself as tactical.
I don't mind games to have weaker parts if they're at least somewhat balanced by other stronger parts. As far as I am concerned, the sum of the whole in FM5 remains strongly negative. There are better tactical games out there, on consoles, not to mention on PC, not to waste your time with this game (and probably the whole series).
TLDR;
Front Mission 5 = over-hyped, as is probably the whole FM series