YMMV / They Are Billions

• Awesome Music: Some of the tracks are pretty epic, courtesy of the Bratislava Symphony Orchestra.
  • The preparation before the arrival of the final wave. It perfectly reflects the tense final moments before the incoming doom on the colony, making sure that every side, every path is perfectly defended. Which leads to ...
  • The final wave music really capture the feeling of a gigantic infected wave crashing on the colony and the epic defense of your troops trying to repel this assault, even against the odds of being massively out-numbered. For even more epic points, the track motivates you to keep on fighting, especially on the final mission of the campaign : The Goddess of Destiny. The orchestral version of the track can be found here.
• Demonic Spiders: The Elite Zombies can all apply to some extent, but the two most disliked by the fans are the Harpy (who can hop walls and shred through defenses) and the Venom (as the only ranged enemy in the game).
• Difficulty Spike: In Survival there is a massive difference in the size of the second-to-last and last hordes.
• Game-Breaker: The Thanatos and Sniper are considered hands-down the best units in the game due to their long range and massive damage output. As the Thanatos is basically a AOE version of the Sniper, it makes sense. Most guides to the survival mode, especially on higher difficulties, advocate focusing on these units and a few high tier towers like the Executor and not bothering with anything else once you have the appropriate tech and resources.
  • Worth noting that as patches have happened this is far less universally agreed upon. Some players will instead recommend focusing on Soldiers and Titans. Snipers and Thanatos share the same flaw of being very VERY slow, giving the Soldiers and Titans at least one very clear advantage. It's hard to say which is better, obviously, but both strategies can work at higher difficulties.
  • On the Campaign, there are multiple techs which can make it much easier.
    • Albeit costly and long to invest in all of them, the train techs will offer you every ressource each time it passes on your colony (every 24 hours) which will make booming your economy much easier and building your Soldier Center without having to set a Stone quarry first. And at the end of the tech line is the Artillery Transportation tech which basically gives you free Wasps each day (you still need to compensate their maintenance cost when deployed however ... which is a measly 1 energy and 2 gold).
    • The Campaign tech tree offers a lot of upgrades to the Soldier : more HP (+20% which nets them 144 HP), more range (+1, giving them 6 range, the same as the Ranger), more armor (+20% which means 60% damage reduction, up to 65% with the Nanomaterials tech) and more damage (up to +50%, 24 damage total per shot). This makes the Soldier the bread and butter unit of the Campaign which is both good at cleaning the map and defending the waves.
    • The Shocking Tower receives multiple upgrades as well : 1) two techs which increases its range by 1 each (up to +2, making it 8 range), considering the fact that it hits all Infected in its area of effect, those two techs are massive boosts, 2) the other techs will reduce its energy cost, while not as impressive, it is very useful, considering they cost a lot in energy (20 by default, down to 10 with the techs).
• Low-Tier Letdown: Prior to the 0.8 update The Solider and Lucifer were considered pretty useless.
  • The Solider does more damage than the Sniper, but it's slower, noisier, was originally much more expensive. Its designated purpose as "meat-shield" is superfluous because your units should always be behind walls when large hordes appear. The 0.8 update gave them a faster XP gain rate, higher damage and armor, a 50% resistance to acid and fire, and a 5 hitpoints per second health regeneration rate. Snipers also had their cost bumped up considerably, making them the more expensive of the two units. Many players still prefer Snipers, but Soldiers are perfectly viable as well.
  • The Lucifer is mostly Awesome, but Impractical. It's the only unit in the game that both can't attack over walls and is capable of inflicting Friendly Fire. It's also far too expensive to use as mere Cannon Fodder, which it would seem to be designed with it's inability to take cover. In version 0.8 it got even more damage, a 75% resistance to acid, a whopping 40 hitpoints per second health regeneration rate, and an increased health bar. They are better than they were, being able to take and deal more punishment and are general effective against hordes in decent numbers. However by the point in the game you get access to them basically every unit and structure is good at clearing hordes, and they cost the exact same amount as the Thanatos, who fills largely the same niche (arguably even more effectively), but can do so from safely behind your walls.
• Narm: The voice acting is... not that great. It doesn't help that a lot of the lines are incredibly cheesy.
  Ranger: Taste my arrows!