Best tower defense game I've played to date
And I did a few... The sheer amount of different tasks, goals and challenges alone is enough to keep me hooked for weeks. It's not just 'survive all the waves', there's also tons of alumets to gain, each giving you another benefit. There's challenges that unlock hidden levels, and there's enough incentive to go back to each level and improve your high score. Ask for more monsters, different monsters, more waves or play endurance.
But that's not what makes the game so unique. It's the gameplay. Different gems have different powers, and the combinations are almost endless. At each level you have to figure out what works best. Going for only one gem or one trick doesn't work in this game, unlike most other games I've played.
The graphics improved tremendously compared to earlier versions, and I didn't experience any lag, even with a screen loaded with enemies. The engine is working as it should and even better. Smooth like butter...
One downside : if you open up the game, make sure you don't have anything to do that day. I've been playing for 8 hours straight.
All in all, superb game, and the first one where I actually bought the Premium edition. Those were 5 bucks spent very well! The extras are definitely worth it, and even if they wouldn't be, the creators of this game deserve the extra cash.
Cheers!