It feels like an expansion for Black Flag really. More of the same, a different story and character in a slightly different setting, with almost identical gameplay. The side missions and other content beyond the main storyline are weaker, and the game is noticeably more buggy and unstable than Black Flag, at least on PC. Apart from that, I don't have much more to criticise apart from the usual Assassin's Creed jank. Playing as a Templar is a nice change, but the fact that the gameplay hasn't been altered much really undermines the impact of that.
Quite a fun game, but only if you really wanted *more* of Black Flag's gameplay, and are willing to settle for something slightly less intriguing and less consistently entertaining. I'm glad I got around to playing this one, but if I get an itch for more of this gameplay in the future I'll just play Black Flag again and leave it at that.