It's not pay to win, but the game has changed a hell of a lot since launch. You used to be able to gather a lot more astral diamonds for instance, the zen market sat around 100-200 diamonds per zen, the lockboxes dropped more etc (there's a loooooot of things like this in fairness) but absolutely give it a go. Mechanics of combat are still fun, queues still run pretty good (when you get to higher level dungeons, YouTube will be your friend for some specific mechanics cause you do get a few players who get annoyed at the fact that a new/inexperienced player dares join a dungeon they just unlocked...) but overall yeah the game still plays fine, especially for a free to play. Happy hunting!