Possibly one of my favorite games of all time. I've got 2000+ hours in the game and I've played for over 4 years and I don't plan on stopping.
Brawlhalla is a FTP (Free to play) platform fighting game (like Super Smash Bros.) that emphasizes itself on stage control, movement, and reading your opponent. Combos are also an integral part of the game and can be highly satisfying to watch at higher levels of play. This can make tournaments a spectacle to behold if the players are going after the massive prize pool that BMG (Blue Mammoth Games), the creators of Brawlhalla, provide to most major tournaments and even some minor tournaments. You can almost always find some sort of content on their twitch page (linked here:
https://www.twitch.tv/brawlhalla) if you wish to see what gameplay can be like. They even host events with the community to interact with everyone and recieve feedback for the game.
Now, as for gameplay, its important to remember that the game is free to play and will remain that way so they have to monetize somehow. There is a weekly character rotation of 9 character which you can buy forever by using IN GAME currency accumulated by playing matches and completing challenges. You also have the option to spend $20 and unlock all of the 50+ current and future characters to be added to the game (which is a pretty amazing deal if you ask me). Cosmetics are not necessary for gameplay and have no impact to gameplay other than visuals but can be nice to have if you find a character you really love. Some cosmetics are even released for seasonal events and color schemes for your characters can always be bough with IN GAME earned currency from your hard won battles.
I highly recommend giving Brawlhalla at least a try if you're curious. It won't cost you anything and you could discover your new quick and casual game or a passion for it like I did. (You won't regret it hopefully)
Happy brawling!