Here's a thread that I don't think has been created before but here's the Fire Emblem thread.
Q: What is Fire Emblem?
A: Fire Emblem was originally released in Japan on April 20, 1990 for the Famicom (Family Computer). You guide Marth and his allies through over 20 maps of enemies, as he deals against the corrupt Bishop Gharnef. It has spawned fifteen games, three and a half are remakes, one mobile phone game and two characters, Marth and Roy, famously appeared in Super Smash Bros. Melee*. Over time, the games introduced new mechanics to the games. It is famous for being difficult because originally, if a unit ran out of HP, they usually stayed dead, except if it was a Lord or an escorting unit, the game over.
Starting with New Mystery of the Emblem, you can choose between Normal (units stay dead), and Casual (units come back after the next chapter).
(*as a matter of fact, Super Smash Bros. Melee was Roy's first ever appearance)
Q: What mechanics are you talking about?
A: In the first two games, you had to guess how many units could move before you couldn't anymore. Mystery of the Emblem introduced the arrows to show where a unit could move to. Genealogy of the Holy War introduced the modern support system, which gives bonuses to a linked unit in some games, usually better stats. It also introduced the weapon triangle (Sword beats Axe, Axe beats Lance, and Lance bests Sword). Some games even have the magic triangle, which is different between games.
Q: Are there any advantages/disadvantages to classes?
A: Of course there are. Some characters are locked to a certain weapon, like I'll bring up Eliwood from the seventh game for example. He can only use swords, and not axes, lances or bows. This can be a bad thing because he can end up disadvantaged against certain units. Bow units usually are defenseless against melee attackers, and Pegasus/Wyvern units fall to bow users. These disadvantages can be used against your enemies as well!
Q: Which game should I start with?
A: That's a good question. I'd probably say Awakening or Sacred Stones.
Q: Wait a minute, am I really fighting monsters in Fire Emblem?
A: Yep, you are. In Gaiden/Echoes and Sacred Stones, monsters show up as enemies in some maps. They can be especially dangerous in Sacred Stones because of their unpredictability.
Happy discussing!