Before you read this review, might I say that the demo is worth trying out to get a sense of the actual gameplay, as the only thing it limits you from is building things in the editors and locks you to only a few weapons.
Anyway, Blockstorm is a strange FPS to describe. Unlike most other voxel manshooters / "Minecraft with GUNZ" games that I've tried, the customization and building aspect mostly takes a background role to the combat mechanics inside actual matches, making the FULLY destructible maps feel more like Battlefield than Minecraft, while having the scale of neither. While you can dig your way underground to an enemy spawn and build fortifications, the building side is pretty limited to just doing that, which I sorta like. It makes the game feel more focused and more like an FPS with sandbox elements rather than Minecraft with guns and multiplayer, which doesn't really work well.
The combat is pretty dull at the current stage. The weapons handle like CoD and shoot like Battlefield, but the movement takes heavy influence from Counter-Strike, in that you have no sprint and movement exploits are incredibly difficult to pull off and end up feeling unimpressive. All in all, it's slow. Not clunky, but slow. Respawning back at your base and making your way all the way back to the battlefield can be frustrating at times in a game where the strategy side is a bit underdeveloped, so most players possess the inclination to just look for guys to shoot.
While that hardly sounds like a recommendation, this game still has a few things going for it; the sheer amount of potential and strong creative tools are huge counterweights to an otherwise average shooter, and given that the game gets updates fairly regularly, Blockstorm could turn into a fantastic large scale FPS to the likes of Star Wars: Battlefront.
When in huge battles, the game really opens up. Fully destructible environments that can be rebuilt as resources permit means that the search for cover is always tense, especially in the thick of battle. A well placed grenade can demolish enemy cover, opening them up to hellfire, and collapsing buildings can be pretty painful. The health regen is slow enough that being shot can have an actual impact on your play instead of hiding behind an indestructible wall for 10 seconds. Building trenches and repairing walls with makeshift patches of blocks is a great experiance when you actually get around to doing it, as the gameplay doesn't really encourage you to at the current stage unless your enemy is smart and whittles away at the map default cover at key points. They need to revamp the gun mechanics to suit this slower style of gameplay, since it feels good when it actually comes together.
The two editors, the map editor and character editor, are very strong, and can push the game to even greater levels if a few creative users get their hands on it. I haven't really used the map editor much, but from the levels I played that were designed in them (that being all of them, as the devs use the tool to create their maps) I can tell it's competent. The character editor is really good and quite a bit of fun. It breaks everything into manageable chunks, and you can start from scratch or edit a skin you already have. You can even import and export parts individually and paste them in at any time, as well as select sections and copy them to a clipboard for use later. You want a minotaur head on a small anime girl body? Go for it, nothing is stopping you! Granted, this makes the game look like a bit of a cluster♥♥♥♥ in regards to the player models on the field, but it's nothing gamebreaking (maybe a force player / enemy model option á la CPMA, devs?)
Overall, I've had a lot of fun with Blockstorm, and I hope you give the demo a try at the very least. If the devs make some adjustments to how the combat feels (and MAYBE up the movement speed) and put more emphasis on the strategy side of building, and if the player base allows bigger, more open ended battles, this can turn into something great. I hope to see you in battle, hypothetical reader. I'll be the chick in a bad Christmas sweater with a bow and a giant CRT monitor for a head.