Kingdom Rush Origins is an okay follow up to all the other KR games and it's entertaining enough as a tower defense title, albeit not saved by different towers, enemies and heroes. I suppose that's the main issue with these games; How do you keep making them and keep making them feel fresh and new? There are some things they could do, like add more tiers of tower upgrades, or tweak the hero system, or change the powers you can use, but it doesn't mean that KRO isn't fun to play. It just doesn't feel very new.
The core of the game is still "build towers on specific spots to prevent enemies from reaching another spot" and you have powers like summonable dudes or lightning bolts, and you have a hero that you can move around to kill enemies. If you manage to get a good score on a level, you get stars that can be used to upgrade your different tower types in various ways. Then you go through progressively tougher levels with enemies that get new powers like stopping your towers from attacking or splitting into two continuously. To match that, you get tower upgrades that branch into two choices for each tower with different abilities and upgrades.
There isn't too much else to say, if you've played the previous KR games, you probably know how this one goes. I'm still bummed out by the very limited number of free heroes and the implication of a 7.99$ dude. How many times stronger than a 2.99$ hero is he? How does it affect the balance to play with a premium hero? Heroes are pretty fragile and use their skills as they sit fit, they also add a power for you to use. I wish there were more free heroes to choose from. Also gems, you can buy them and you get a very small number after each map, and they can be used to buy one-use items that probably just throw balance out the window. No need to be good at tower defense if you can just nuke everything for 11.99 (best value!)
Even if the systems aren't completely new, the tower types are fun to try and upgrade, and even if it's a bit difficult to tell which is better in a specific situation, they cover a wide range of abilities you can give to towers in such a game and the progression works okay. The level design - much like the previous game - leaves a bit to be desired because while you can only place towers in specific spots, sometimes the map will change just before a wave and your existing towers will kinda be left there doing nothing. Maybe some indication of where the enemies will come from and the path they'll take in the upcoming wave would be useful?
Anyways, if you've enjoyed previous KR games and want to play another one of these, Origins is pretty much okay. It's also a good tower defense game on its own merits and you'll be able to sink a few hours into it.