I played both Plants vs Zombies and Bloons Tower Defense 6. Both had very different takes on the genre- they were both very evidently tower defense games (you had to use characters to make sure enemies did not reach the end of the line), but PVZ focused on organization, breadth, and shoring up different parts of the line, while BTD6 focused on stacking defenses in a mostly single track line and depth of tower organization. BTD6 allows you to upgrade your towers, while PVZ does not.
I personally am a huge fan of this genre- I love games that build up, so you see your progress in front of you and see visually how your progress has grown. In other games, your progress may be in terms of a score or an attribute of your one character- maybe your character has gotten bigger over time, or has a higher health bar. But the attraction to tower defense games for me is how the game itself is built visually off of how evidently you can see your progress in front of you- going from a level 1 dart monkey or a single peashooter on a huge field to a conglomerate of stacked up super monkeys or a field of well-placed plants. Tower defense games use this as a primary factor- allowing you to build these strategies in different settings and modes, giving you endless choices to pick and choose from (for PVZ- it’s the types of plants you choose for a level and the special modes and zombies, for BTD6- it’s the tracks and the upgrade paths) every time.
This intensely visual experience that focuses on long-term and in-depth gameplay is what defines the experience for me and is what separates this genre from others is synchronizing tower placements and harmonizing their attacks, as well as making sure all areas and types of enemies are covered in my lineup.
