Tower defense at its best. Being able to place your towers in such a way that it forces the baddies to take longer paths is extremely enjoyable and challenging.
- Block baddies just as they're getting near your cores, forcing them to re-route.
- Bounce a train of baddies back and forth between two paths by repeatedly opening one and blocking the other.
- Unspent money earns interest so if you build just the towers you need, you'll have even more money later on.
- Create "kill zones" with your most powerful towers + slowing towers + bonus money towers to maximize efficiency.
- Cool story with some great DLC (The Portal cross-over DLC is top notch)
- Alternate modes/achievements will keep you playing for a long time