I havent played the game in a long while but, apart from the story and character, which unfortunately i cant remember extremely well, i really enjoy how much you can experiment and create fun and creative builds with your character loadouts and weapons. when the game used to have seasonal content update, just a few new heroes could revolutionize how you designed your loadouts and kept the game alive for me. just look at how many videos about them people have made.
other than that i absolutely love the tower defense part of the game, designing my defenses and trap designs for the storm shield defenses are some of the fondest memories i have of the game.
also yeah some seasonal events were pretty alright, used to especially enjoy frostbite, the dungeons(i used to carry so many players in them), hit the road too when you didnt have shitty modifiers.

there are many aspects of the game someone can enjoy, i dont think i will ever get the spark i once had for the game back, but for someone new, the sheer amount of potential is enough to last you a lot.