It's an excellent concept, but the difficulty curve needs work. Very early on I made a web-design that pretty much instant-kills enemies, with nothing for me to do but occasionally walking over to the edge of the web to collect the loot. In fact, I kept the game running while getting something to eat without any danger to myself. Currently up to 1000 kills, no sweat.
I could see many ways to add to the game, such as ranged enemies that try to stay away from you and you have to lure into the web, enemies being able to destroy the web (or if that's too complicated, drop slick goo that negates the damage from the web where it is), or jumping enemies that encourages you to make a specific web pattern to catch them easier.