Recommend me a tower defence game

[DanF]

Dungeon Warfare 2 on Steam

Become a dungeon lord to defend your dungeons with the deadliest of traps and insidious contraptions against greedy adventurers and wannabe heroes.

store.steampowered.com

this is a bit of a hidden gem, looks rough but really fun to play and has some towers and tactics fairly different to the normal ones

 

[coupe69]

Another vote for Defense Grid 1 & 2, I've played both of them to death, and they are really addictive.