Boxhead: More Rooms

Objective: Kill Zombies. Shoot up zombies and their demon buddies using a variety of weapons in 8 different levels. I veer between loving and hating the demons. As a game designer, I like that they keep gameplay from stagnating because they require a completely different strategy than zombies. As a player, I hate them because often one stuns you and hits you until you die — so you effectively have only one hit point. Still, I really enjoy this game.

Flash Element TD

Build and upgrade towers to keep streams of enemies from taking away your life. I really like the balance between earning interest, building, and upgrading. I think this game couldn’t get simpler and stay fun; each research point is a serious choice. I haven’t beaten the final level (39).

Onslaught

A unique and well-polished tower defense game, Onslaught has a great upgrade and combo system. Keep the How to Play page open in another tab for at least your first few games, this is complex. There’s a new version in beta, but I believe it’s mostly just a cleanup of the internals. I didn’t find any differences in gameplay after a few minutes of playing.