Image via WikipediaTechnically, the full title is "Sid Meier's Civilization IV: Defender of the Gates". However, it's way too long. So it's just Civ 4: DotG, or just DotG from now on.
Despite the name, this game is only peripherally related to the CIV 4 franchise... as it really is a tower defense game. However, the eras, the units, and the techs, and the upgrades all are from Civ 4. You control one of four civilizations (America, England, Russia, or China). You must build defenses to protect your empire against 50 waves of attack from the Huns... who managed to kept pace with your empire. Can you keep your civilization from being conquered and trampled?
If you haven't played tower defense, this is the premise... Enemy units come through a fixed path, and do NOT shoot. You must place defense towers/turrets along their path to destroy the invaders. The problem is invaders gets stronger each wave. Each wave, the Hun leader will insult you, promise to crush you under their feet, and how their weapons are unstoppable. They start at a mere 10HP, and move "slow". By the end, they will have THOUSANDS of HP, and move at fast or better. However, for every invader you destroy, you are rewarded with certain amount of gold, with which you can purchase more towers, upgrade the towers and/or other abilities. The objective is to last as many waves as you can, preferably all 50. The waves will vary somewhat, as some waves have special abilities. They can send a lot of weaker units, or one super unit (a boss). They may even send units that fly (so only certain towers can engage them) or even units immune to some of your towers. Remember, let as few through as possible.
This game adds a few wrinkles. Each era also gives you certain tech points, with which you can unlock technologies similar to Civ 4's tech tree, and those technologies will enable certain upgrades and more powerful towers, or affect the cost of towers, and other effects, such as pay you X amount of gold per civilian killed. Each civ starts with a unique advantage (America gets 1 extra tech point at start, China gets 10 extra citizens, etc. ). Each invader that gets thru will kill 1 of your citizens though a boss unit may kill more (and some may even steal your gold) You start with only 20 citzens, except China, which gets 30. When you run out of citizens, the game is over. You can also buy a new gate, make the gate stronger, and so on. A gate will delay the enemy incursion by X seconds, enough to let you upgrade/add/sell towers. With the right tech, the gate itself can be made stronger.
The gameplay is fast but fun, as each wave will only last a few minutes at most, and it autosaves, so you will lose at most ONE wave of progress. And there is not a lot of button pushing. It's a bit like an experiment... You set it up, and watch the results. The problem is it's possible to dig yourself into a hole that's impossible to dig yourself out of. The difficulty at the final era goes WAY UP, so unless you've save up the money from earlier eras and let it earn interest so you have plenty of $$$ (like 1000 gold or more) to upgrade turrets for the final era, you will not last more than 5 waves in the final era. And that's a big problem. Yes, gold you did NOT spend actually earns INTEREST, and economy upgrades will increase those interest rates.
There really isn't much sound in the game, nor does it really need much. There is a bit of music, but only in the menus, and that can be turned off. The music is not annoying, believe it or not. Graphics are quite good as all units are unique and animated nicely. Each tower also looks different, from upgrade to upgrade. The terrain looks good, with the path, ground, and occasional trees. The only nitpick is when the towers are packed together it may be difficult to pick one out to upgrade and whatnot. The menu system is clear and concise.
All in all, this game is quite charming, if they can just fix those final levels so they aren't so darn difficult... It'd be hall of fame material. And the help file is lacking, as there's no list of turret capabilities. A lot was found by trial and error. And the top level tech is WAY too expensive. As it is, I can only give it an 8.
HINT: to survive the final 10 levels (more like 7, as the 41-43 are doable) you need to have a LOT of money (like 1000 gold) left over from earlier levels. Somehow, you need to figure out what's the MINIMUM amount of turrets needed to survive each level. And build ONLY THAT. The trick in accumulating money is by using the "interest". Remember, every piece of gold unused earns interest. So the objective is to leave the max amount of gold possible unused, so you earn max compound interest, yet still have enough firepower to destroy most of the enemies.
HINT: Get as much use out of EACH turret/tower as you can. Put them where they can attack the enemy MORE than once (like when the path crosses back on itself). This allows you to minimize the number of towers you need to place, thus saving you $$$. Second best spots for turrets are corners, but not just right at the corners, but maybe slightly back, depending on the range of the turret, so they cover the max amount of the path possible. Cover the path as much as possible. Nothing else matters.
HINT: Cold turrets, esp. when upgraded, slows enemy units down as well as hurting them. Put the cold turret(s) first when in groups, so the rest of the turrets have max time to use the slower speed of the enemy to do more damage.
HINT: The rock/boulder/powder/cannon series of towers will engage air type enemy, but they don't do as much damage as an anti-air tower. On the other hand, the stick/arrow/crossbow/gatling type tower do NOT engage air type enemy at all, except bosses.
HINT: It's better to have a "few" of the strongest turrets, than a lot of the weaker turrets. The final turret upgrades gives you gatling gun (beyond crossbow) and cannon (instead of powder), and air 3 (instead of air 2). However, those turrets are EXPENSIVE (gatling is 185, cannon is 280, and air 3... I think it's 380), and that's the UPGRADE price. That's why you want to save a LOT of money from early on. So you can afford these at the end. Believe me, you will need a LOT of max upgraded turrets by the end... all gatlings, all cannons. I ended up using at least two cold 3 towers, at least 2 flame turrets, and at least 4 air 3 turrets, in addition to all the gatling and cannon turrets that are already in place. There are BETTER upgrade beyond that, but they're not strictly necessary.
Overall rating: 8 out of 10
Pros: tower defense melded with Civ 4 tech tree and upgrades! easy to learn, hard to master
Cons: bad difficulty progression at the end, only peripherally related to Civ 4, not enough info about the towers
ADDENDUM: as it turns out, the final level upgrade is absolute essential in surviving the final wave. You *could* do without them, but it makes the game that much harder. The final pulse tower puts out 800 damage every half second, and is effective against both ground AND air targets. Put up two of these, plus a missile turret, and nothing will get past, not even the final razorjets. Of course, one cost $900, and the other $1000. So you need $$$ saved up.
Forget about other tech upgrades. You just need stuff that gives you higher tech, and higher interest rates. Nothing else matters. Oh, and you'll need physics and chemistry to get cold turrets, which will get you to pulse and missile turrets.