CastleStorm is a weird mix of Angry Birds and strategy RPG elements. The goal of most levels is the same; to destroy the enemy's castle. To do so, you fire projectiles, spawn units, use magic and try to complete special objectives to gain more money and more stars. The game has some fine ideas but it's a bit unsure of what it wants to be and so it doesn't do anything particularly well.
Your basic way of playing this game is to use the mouse to shoot things around. You change your equipped weapon with the numbers, you can also right click to summon units, provided you have enough food (a resource that regenerates over time) and still use the number keys to choose which ones you get. Using the middle-mouse button will change your hotkey bar to spells. This game controls really bad, I wish they'd made three hotkey bars, one for projectiles, one for spells, one for troops, let me use QWERT for units and ASDFG for spells. Left click, right click and middle mouse click aren't great ways to go through different things and I've summoned units by mistake more than once.
Between levels, you can upgrade your projectiles, troops, spells and castle rooms. I love upgrading things but I felt underwhelmed by the choices in CastleStorm. You get increased statistics (damage/cooldown for projectiles, hit points for units, effects for rooms) but you never can change the game to play the way you want it to. It would've been neat if you could get upgrades that alter projectiles, or even choices of upgrades (make the tri-stone split into five or just be a bigger rock that can't split). And most of the choices are weird, I almost never used anything but the basic projectiles, one or two units and very few spells. Spells feel useless, jungling between different unit types feels pointless and I just spammed the same attacks over and over, and won.
To make things weirder, you can only use troops defined by your castle and the different rooms (passive bonuses such as more gold per kill, more food capacity, army size) are all set on a per-castle basis. Why not have one castle in which you can change the rooms and barracks? As it was, I just tried to have units I used and all the bonus rooms, not even looking at any other particularity my castle would have. You can edit their layouts to add more stuff, but I never came close to losing because my castle was under attack, so I don't think it's that important.
The hero units are very awkward, they're summoned for a while and then the camera zooms to your guy and you move and attack manually. The movements are stiff and you can get knocked out of most of your attacks. You have a super move that needs to be charged up and projectile attacks but it's mostly a better plan to just shoot things instead of taking 30 seconds to control one dude. Make the hero automatic or make the controls tighter, give heroes special abilities to make them unique instead of slightly stronger foot soldiers, have their upgrades be more than stat increases.
CastleStorm is in no way a terrible game but I'm unsure what it wants to be. It forces you to stick to certain things (only spells, only projectiles, only troops) so often that you wish you had more straightforward destroy-their-castle levels along the way. It's fun to shoot things until enemy units have so much HP that you need to pelt them forever before they go down and the cooldowns on some heavier weapons is crazy. It's fun to spawn units except they die really quickly, spells could be good (a barrier that stops enemy projectiles, direct damage, invulnerability) but they're so annoying to use (why not make all the spells work once used? It would be better to have global effects of smaller magnitude or having the hero/barrier placed automatically in the middle of the battlefield instead of having to click to choose a spot for your spell to go)
After a while you unlock the viking campaign, and it looks very familiar to the soldier campaign. You get a few good units (I only used druids? Like, 100% of the time) and some neat weaponry, but you still have explosive projectiles, projectiles that split, projectiles that home, a barrier spell, a hero, direct damage abilities and almost the same castle rooms. It should have been a bit different and crazy.