I like the concept, the graphics are spectacular, and I think the game is pretty innovative, but the levels get progressively slower as time goes on, and it eventually becomes pretty much unplayable. I'm not sure why that is; might have something to do with the particles causing a long-term slowdown, because it doesn't look like there's too much more on the screen in later levels; at least, not enough to cause that great of a slowdown. But it's definitely the one thing I'd try to fix.

Looks like I'm part of a crowd here that thinks this is a pretty tight defense game, but it slows to an absolute CRAWL sometime in the level 20's. I've tried this with two different computers, Firefox and IE, and I even tried downloading the standalone, and I get the same results. That to me is a major flaw, so I'm knocking off several points for it. I'm not sure what it is, but Oroboros has the same problem and I've noticed that both games use a lot of particles, so maybe that's causing the long-term slowdown.

Been meaning to review this one for a while. It's a really nice game and challenging, but its downfall is that once you discover the one truly effective strategy (in short, a shitload of fully upgraded ice towers), every map except impossible plays out almost exactly the same.

I think that any sequel you make for this should make room for more diverse strategies, and also some more interesting maps. All the current maps have point symmetry, which tells any savvy player that any effective turret formation can simply be duplicated on the other side; asymmetrical maps would force players to adapt to the "landscape" more to find the best places to attack creeps from.

For beginning or struggling players, here's my usual strategy. I'll just count grid spaces, starting from the top left as (1,1), for positioning:

Easy:

1 Level 2 MG (machine gun) at (7,7)
Upgrade MG to level 4
Build FT (flamethrower) at (9,7)
Maximize MG and FT
Build and maximize second FT at (13,7)
Start building IT (ice tower) in the rectangle between (9,5) and (13,9)
Once IT grid is complete, sell MG and FT and build as many LT (light tower) as possible, anywhere that gives good coverage.

Hard:

1 Level 2 MG at (6,7)
Second MG at (16,7), upgrade as needed to prevent creep escape but focus on original MG and FT's
Upgrade MG to level 4
Build FT at (7,7)
Maximize MG and FT
Build and maximize second FT at (15,7)
Start building IT in the rectangle between (9,5) and (13,9); may not need to completely fill in
Once IT grid is complete, sell MG and FT and build as many LT as possible, anywhere that gives good coverage.

Very Hard:

1 Level 2 MG at (9,7)
Second MG at (13,7), upgrade as needed to prevent creep escape (this will require quick reaction time; depending on the random damage range, a few creeps might escape no matter what you do)
Upgrade both MG's to level 4
Build FT at (10,7)
Build second FT at (12,7)
Maximize MG's and FT's (cheapest upgrades first)
Start building IT in the rectangle between (9,5) and (13,9) (noticing a pattern here?); may want to sell MG and FT to fill in IT grid as much as possible.
Once IT grid is complete, sell MG and FT and build as many LT as possible, anywhere that gives good coverage.

Impossible:

You're on your own. No strategy I've used has gotten me past the round of large white circles.

Quick notes on alternate strategies:

I've advised not upgrading the LT's because building additional level 1 LT's is more effective due to the stacked armor piercing. Really, though, your IT grid should eventually freeze all the creeps in one place, at which point it won't really matter what strategy you use to finish them off.

Lightning towers work fairly well by themselves, but their stun ability will sometimes cause other turrets to target the stunned creep instead of the frontmost creep, which may cause your IT's to let creeps through by the droves.

I've never gotten much effective use out of the two splash damage towers (plasma and void).