I mean, yeah, Garden Ops is a horde mode, but I wouldn't liken it to Dungeon Defenders. Dungeon Defenders felt so flat compared to PvZ -- it's much more involved and strategic.
The real meat of the game is in the competitive multiplayer which has deathmatch and objective (plant the bomb, domination, conquest) modes. There are four classes per side (four plants, four zombies), but about 5 variations per class, meaning that you can upgrade your Pea Shooter to shoot fire, ice, or poison bullets through unlocks. The same can be done to every other class.
It's actually a surprisingly deep experience for those willing to devote some time to it (which you should -- it's fantastic).