Defense Grid - please god in Heaven someone help me

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This is only my second tower defense game after Plants vs. Zombies, and I picked it up after hearing Fraggamemnon's recommendation on The Borecast.  It starts off easily enough, but now I am completely swamped and destroyed on the 6th or 7th mission (called "Focal Point"). 

Essentially the map is a series of interconnected islands, wherein you are supposed to route the enemies along a convoluted path across many different islands, so as to maximize the time they are exposed to my defenses.  I don't have much of a problem creating an intricate maze or a devastating AOE chokepoint, but nothing seems to work.  I end up spending all of my resources merely routing enemies and I don't have the capability to upgrade anything or invest in heavy firepower.  So when the big big baddies come out they laugh as they slowly trudge through my gauntlet of piddly Lvl1 turrets and lasers, eventually stealing all my power cores in the final waves.  Obviously there's a solution to all this, but I don't really understand how to prioritize routing versus firepower and I'm pretty aghast at how the game has ramped up to a very nasty difficulty level.  It was only $2.50 on Steam so even if I quit it entirely I wouldn't feel cheated, but I'd like to figure everything out without resorting to cheats.

[Fragamemnon]

I've still got the game installed. I'll give the mission and a go real quick and see if I can give some pointers.

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Part of my problem is that the vast majority of enemies are vulnerable to guns and cannons, and there's only a handful that are weak to lasers......but that handful of enemy types (particularly the super-fast elongated mobs) are utterly devastating.  So many times they can just cruise through your slowing Temporal Beacons without getting hit, my only counter to them is the orbital laser.  I feel obligated to build lots of guns, so I never have enough lasers to take them down.  Plus the lasers are twice as expensive as the turrets, so it's difficult to establish laser defenses early on because you are do focused on building cheap barriers to properly route enemies.  I feel as though there's some point in the battle I should start selling off my guns for lasers, but resources are so constantly tight that the opportunity never opens up.

The map layout is wide-open and it's very disconcerting to be given such a huge sandbox so early in the game.  I feel like I haven't really even learned the basics and the game is already commanding me to demonstrate a pretty high level of mastery.

[Fragamemnon]

You can't upgrade the turrets in that mission? That's odd-I am able to upgrade gun/laser/temporal turrets there, all the way to level 3. I have gun turrets through Tesla turrets unlocked for this mission.

Anyway, the first thing to do is block off the first island they get to after leaving their entrance. Force them into the middle island, where you can then prevent them from going up the map  with another wall of L1 gun turrets. From there, you can set up a nice kill zone on the next island with a temporal, a laser, and an inferno (for maximum burn damage) tower with some gun turrets. It also allows you to set up some cannon turrets on neighboring islands near the end of the mission to deal with the higher-HP foes.

Here's how I ended up at the end. The north island is blocked so they have to pass through that nasty island twice. One of the keys here is to also use your laser if one of the fast ones at the end looks like he is about to pick up a core-they basically act as carriers for the really heavy armored foes who will then use what they drop for a shorter path to the exit.

[Fragamemnon]

There are lots of shield dudes in this mission (if the shield is up, laser does nothing) and multiple lasers are almost always if I remember right redundant since it's the burn damage that they get hit with that's as much of a deal as the direct DPS and that (to my knowledge) doesn't stack.

Guns are good and are bread and butter throughout the game. They will also ensure that fliers on this mission die (cannons are good for this too, but cannons are really for dealing with armored waves like you see at the end of the mission).

[Cormacaroni]

I bought this for $2.50 as well yesterday (AFTER my 'final tally' for the Steam sale) but I'm terrified to play it now

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I can upgrade my weapons, my problem was that I just spend so much just laying down units to establish pathing that I never have the resources available to upgrade weapons that much.

It looks like you've got everything concentrated on a few islands though, whereas I was focusing on making a path that stretched across every single island.  Maybe better guns on a more concentrated path is what will work.  I will give it a spin when I get home tonight.

[muckhole]

Here's a decent vid that shows what to do. Pretty sure it's along the same strategy that Frag laid out.

[youtube=560,345]FXu7QHGp8hw[/youtube]

[Fragamemnon]

The temporal turrets are really bread and butter to this game and help encourage setting up efficient killzones by (when possible) forcing the enemies to cross through the temporal turrets and its field twice. Setting up that one megakill island that they have to cross through twice is something you'll do a few times throughout the campaign.

There's more than one way to do this mission-I was able to complete it with a different path entirely-but the one in the screenshot/youtube above is the optimal placement (IMO).

[pilonv1]

I use a different route than frag too but the idea is the same, making the mobs travel as far as possible. Throw in a few temporal towers (which are the best in the game) and you should be fine. It seems that using more towers than upgraded towers works best in this game.

Meteor towers are awesome too.

[Great Rumbler]

Focal Point ate me for dinner about half a dozen times, maybe more. I don't remember what I did, but I finally smashed through it.

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For what it's worth, the rest of the game is not quite as bad.....but I did have to look up strategies for almost all the other "sandbox" style maps that require you to determine enemy pathing.  I liked the game a lot better on maps when the enemy path was static and you just set up defenses along the roadside.  All I ever had to use was guns and cannons, really.  I'm not sure if that means that game is hugely imbalanced or it's just a testament to versatile design.  Once I gave up on about half the arsenal everything got much much more easy.  Build guns, upgrade them frequently.....maybe throw in a Temporal Disrupter if you get a very dense, tight killzone established. 

There's actually a video on YouTube of someone doing the final level with nothing but cannons and a couple missile turrets.  None of the cannons even get upgraded beyond level 2 and at the end he has like 40,000 resources - insane.

Any other tower defense games I should try?

[pilonv1]

The ability to finish a level with only a few towers ties into the scoring. You get more points based on the interest your money collects or something, so placing less upgraded towers gives you a better score. So that's why it's also possible to complete some levels with a small variety of towers.