Games like Sequence are the reason Kickstarter and the Indie Game movement exist. It's not a perfect game, not everyone is going to enjoy it and it will never receive a lot of fame and recognition. However, for the niche audience that can appreciate it, Sequence is a game like no other.
The closest thing I can relate Sequence to is Puzzle Quest. The game doesn't play like Puzzle Quest but what that game did for Match-3 games, Sequence does for the rhythm genre. The base game has you traveling up a tower by fighting enemies, collecting their dropped items, and synthesising items such as keys, weapons and armor. Battles give you experience which will level up your stats while armor and weapons are equipable and can also improve your abilities.
Where Sequence differs from the average dungeon crawler is that combat is played out by putting you in a rhythm system similar to StepMania, if you're using a keyboard, but with three separate boards. One board is defensive, one board is for building mana and one is for casting spells. On the first board, any notes that you miss will count as damage against you so catching them defends your HP. The second board will have a constant stream of notes. Missing them doesn't hurt you but catching them restores your mana which you need to cast spells. The last board stays dormant until you cast spells, the only way to damage your opponents. When you cast a spell, it takes mana and makes you complete a short rhythm sequence. Failing it causes the spell to fail but completing it will cast that spell. While it can be a lot to juggle at once, the game does a great job of teaching you and ramping up the difficulty slowly in order to build your skills both in game and out.
The gameplay by itself is fun for a while but as the entire game is built around grinding items and EXP, it would get boring very quickly if it weren't for the well written story pushing players forward. The tone reminded me of The World Ends With You in the best possible way, but felt wholy unique. Your main character finds himself waking up in a tower with no idea how he got there. The voice of a girl named Naia tells you that you are stuck in this tower/game and you will need to make your way up 7 floors to escape so off you go. While there are some predictable moments, the story as a whole never becomes too transparent and despite a few moments when I swore I was done after one more battle, curiosity kept me pushing ever forward. The characters are all voiced as well and while none are particularly mind-blowing, it's a nice touch and the quality stayed consistent throughout. If you do find your bar set particularly high in regards to VO quality, they do have an option to turn it off as well although I doubt this will be necessary for most people.
That's not to say the game isn't without it's rough spots. For a music-based game, Sequence has a surprisingly limited soundtrack of only about 10 songs that show up in battle. This means several monsters will have you playing the same songs repeatedly. Thankfully, they aren't bad and some of them I didn't mind repeating but considering each monster all but requires multiple playthroughs anyway, don't be surprised if you wind up hearing the same song 10+ times. As that suggests too, the gameplay is simply too grindy and while item drops are pretty common, it can be irritating when you need one specific item and have to fight the same monster over and over just to move forward. Finally, the song balance is a bit odd as by the end of the game, the length of the song decided more battles for me than my HP did. It felt like very artificial difficulty (you lose if the song ends before killing the enemy) and it would have been nicer to have some of the songs be just a bit longer, especially in Floor 7. Depending on your strategy, you may not have a problem with this but it showed up several times in my game.
Overall, if you're looking for something different and enjoy music gameplay, Sequence is worth a shot.