Defense 2 follows much in the footsteps of its predecessor in the tower defense genre to bring you a game about protecting cores from aliens by building towers on their paths - sometimes even making the paths themselves. I had a good time with it, even if I was perplexed by some of its systems and had to tone the difficulty down to Easy in order to enjoy it. The story also kept me interested, which is a nice thing for a tower defense game where characters are usually not a huge presence.
The menu is a bit weirdly built; You unlock levels in packs of four - or are they all available from the start? I'm not even sure - and each level has a ton of different modes you can play them in. Do you get anything but leaderboard fame for completing these? Are any unlocks tied to the completion of special modes? Is anything tied to the skillful completion of story missions, for that matter? You're graded on your final score - and can be given a bronze, silver or gold medal for your troubles - but do these do anything? If they do, it should be more surfaced, if they don't, what would be my motivation to redo these levels in ten different ways?
Towers are more or less similar from the first game with a wide range of cost-to-effectiveness ratio, special abilities and three level of upgrades. A new thing in DG2 are Boost Towers; Towers that cost very little that you can build on. They're pretty much required since they improve your towers and unlock upgrades for them, so you could say that building every tower necessitates an extra step, it would've been good to be able to build boost towers below an already built tower to give more options. You can upgrade your towers with abilities you unlock in some mysterious way, these range from 20% more damage to shields to damage over time - to being able to target the strongest enemy in range, which is weird to give a targeting option as a power-up. You also can choose a character's special skills, which are on cooldowns and are mostly left to playstyle.
Enemies have a wide range of special abilities and counters; Some have shields, some turn invisible, some go very fast in straight lines, some spawn more enemies when you defeat them. The game introduces them very clearly, but then as the game goes on, I found it very difficult to know exactly what enemies did. Sometimes in maps where I was having no issues, whole waves of foes would just zoom by without me figuring out why. The levels are fine, even if - as usual - I'm not much of a fan of tower defense levels where you have to figure out paths as well as tower placements. DG2 isn't exactly freeform, so that's fine with me. I mostly used Meteor and Missile towers - some levels were also completed exclusively using them - towers that shoot powerful but slow projectiles across the map.
Speaking of towers, I really am not sure about the usefulness of the 'Score Boost' upgrade provided by boost towers; You can boost the damage of the tower stacked on top of it, or add a wave effect that disrupts invisibility and shields - two useful thing - and then, instead of adding another 'useful' effect such as increased range or fire speed, you have 'Upgrade Score Boost' which makes it that nearby killed enemies give more points. Are the points that important? It's not like you're using these points to build more towers and there is no 'point shop' to buy upgrades between levels. You also can move parts of some levels around but that felt superfluous to me, are these moves always good strategic choices? If they are - and I should always make them - what's the point of having them?
In any case, DG2 is a fun little tower defense game that I stuck with for quite a while and I had a generally positive experience, which is not too unexpected, with my love of that genre and the overall quality of the title.