The folks at DeSync Studios liked the Line Tower Wars mod in Warcraft 3: Frozen Throne so much that they made a game based on it. That's not all their new tower defense game, Unleash, has to offer, but for my money it's the most promising bit.
For the uninitiated: Warcraft's Line Tower Wars mod turns it into a tower defense game where you build your own paths. (There's also a similar mod for Starcraft 2.) As opposed to tower defense classics like Bloons or more recent fare like Sanctum, you don't just place towers on a pre-existing course. Instead, you build the path enemies take to your base using walls and even the towers themselves. That's the vibe I get from Unleash: your base is here, enemies come from there, and everything in-between is up to you.
Unleash recently entered Steam Early Access, where DeSync expects it to stay for six to 12 months. The studio says the finished game will have more tower and monster variety, as well as spiffier online services, but the core game is already playable, including the eight-player multiplayer. Apart from the Line Tower Wars mode, there's a standard tower defense mode and a go-crazy sandbox mode.
