Rogue Legacy is a roguelike platformer with plenty of very interesting mechanics. The way your new characters come to life when your old ones die, the exploration of the castle, the options you have to customize your characters, everything is almost flawless. I've found some issues here and there that I would maybe tweak a little for the way I like to play games but otherwise it's a blast.
Rogue Legacy isn't a Metroidvania by itself, you don't unlock new abilities to allow you to get to new parts of the castle. The game basically puts you back at the beginning of a randomly-generated fortress (with a forest to the right, a tower above and darkness at the bottom of the map) and you need to defeat four bosses before a door opens and you are allowed to defeat the last boss and end the game. You aren't going to do this on your first try (because the game gets difficult fast as randomness could put you against a bunch of difficult enemies on your first run) and when your character dies, the next generation takes its place.
Between runs through the castle, you get gold that you use to go through a skill tree and buy equipment to make the process go easier the next time. Each time you buy a skill, your overall level increases and so does the cost of other skills, this means that if you decided to max out a skill like maximum mana or carrying capacity, everything else would get really pricey because you got to level 75, and maybe you wouldn't be able to improve anything else. I'm not saying that people usually will try and max only one thing first but the fact that all skills increase the cost of other skills seems a bit weird. You can't really reset your skill, some of them are expensive and you don't keep your gold between runs, so maybe lessen the increase in cost? When you get into the castle, you give 100% of your gold to Death itself (can be reduced to 70) and you also have the option to keep the castle's layout the same for 30% of all the gold you'll find. This is useful if you don't want more gold (chests will stay opened) but want to defeat a boss or try for a fairy chest.
Exploration of the castle is punctuated by mini-games, challenge rooms and other silly things. You also find diaries of some past explorer that went into the castle, and there are 25 of them, little thing I found weird is how if you just die and restart in the castle part constantly, you'll read about how they explored the forest and the tower and the darkness and all that even though you've never set foot there, they should probably have left these entries in those respective areas. Fairy chest have challenges that you might not be able to complete with your current set of abilities and therefore need to think about locking down the castle's layout, or randomizing it and hoping that the next fairy chest challenge is better suited for your character. You also find piles of gold in some chests and equipment blueprints in others.
Unlocking equipment and runes won't give them to you, they just allow you to buy them at the blacksmith. Luckily, they stay unlocked between runs, so your next character might be a little bit more powerful. You need to mind your carrying capacity, otherwise you won't be able to equip the next thing you get. Equipment affects your basic stats such as health, damage, magic, with some specific pieces giving you bonuses to other stats like critical hit chance and damage, life leech, and so forth. You can have five runes equipped at a time and their effects stack, ranging from double jumps, sprint, more gold per coin, mana gain after killing an enemy, you'll need to find them and buy them, but their effects are useful and change how you play the game, but you'll never need double jump to get somewhere, so it's just a question of taste.
Each character has random traits and one random spell. There are a few spells I don't like but traits are all manageable. Some traits are weird like making everything in black and white, hiding your health bar, making you knock enemies back all the time or give you MP when you break things. I think there should be more trade-offs for these traits, the one that make the edges of the screen blurry could give you more crit chance up close, not seeing your health bar (you don't feel pain) could give you damage reduction, getting MP when you destroy objects (ADD) could remove your MP if you leave a room without breaking everything in it. But otherwise they make each run slightly different and you'll be surprised by the random silliness they bring.
Rogue Legacy is amazing, it might be a bit difficult and you might die a lot at the beginning of the game but you can upgrade your characters to your liking and progress through the end of the game, little by little.