I like it
Well since I discovered this was out on Armor games i've been playing it for a while each day. It was fun at first but after I finally got to the last level and started finishing up all of the modes i've gotten bored of it quickly. Now I only play a few levels per day. It's an amazing TD game but now I can only handle it in small doses.
Graphics as usaul are amazing. Probably the game's strongest point. Story I don't know much about since I just skipped those parts. Some NPC's would have helped to make some levels more interesting. Moveable heroes (like in some other TD games) may be a good addition if you decide to do a third.
Tips: Try redistributing your skill points if you're having trouble with a level. Play the triple experience levels as they become available to go up levels more quickly. Also, some skills are fairly redundant and do not need to be invested in at all. PM me if you're stuck and need more advanced tips.
Despite Zero's flaws, it's still one of the best flash TD games available. I've come to think that it is meant to take a long time to actually beat every level and if that's the case then this is surely the longest-lasting flash game ever made. I'll continue to play it a bit every day until i'm up on that high score list.