Sublevel Zero I'd not really heard about until the release on GOG. I was rather captivated by the shiny looking graphics of the game, and that it was promoted as a single-player procedural rogue-lite permadeth 6DOF* game. My first experience with 6DOF was the 1998 game Forsaken, rather than the Descent series, which I also only played once they had their GOG rerelease in 2008.

In short,it hit everything I was looking for. With the Descent reboot turning into a Multiplayer focus first game, this one would scratch the genre itch. (At the time of typing this up, Overload is in kickstarter and should also bring to my gaming tastes something enjoyable.

6DOF: Six Degrees of Freedom. A shooter genre where you are not stuck to the ground plane and can look and move in the full 6 axis

The game actually makes my PC run quite warm and I've had to put it aside during the roasting summer days here in Australia, but I can see myself returning when the weather cools down. But it runs smooth and I rarely had any loading issues.

Right away, the game just oozes the style it is going for. A retro/pixel look plastered into a modern 6DOF game. With great use of colour, lighting, and transparency. Initially I saw criticism of what they were attempting and a lot of this went away once people saw it running. Retro/Pixel has been a bit overdone the last couple of years, made harder by games in a long development cycle that started when it was cool, turning out old by this point.
Thankfully Sublevel Zero has its own retro style. Nice blocky and angled lines, objects, and enemies. All with a great winding style in long corridors separated by small and gigantic open rooms. The UI feels easy to navigate and add/deploy/craft equipment too. The into story segment felt a little unfinished in comparison, and while you can come across little datablocks in the game they appeared more for flavour than anything on a grander scale.

The first level starts off simple, you are dropped into the highest level and have to find your way too a giant station core and destroy it. Enemies at this stage have low HP and take some time before they can face you to shoot you.
They do pack quite a bit of firepower though! This is not a game where you could stand staying in their line of sight for long without seriously getting damaged or killed outright. Sometimes you even get unlucky and encounter 3 or 4 of them huddled in a small room behind a door that you need to shoot or approach to enter. Requiring emergency evation to get out of their way before you lose. On the first level. Yes, this happened to me too.

Later levels had the introduction of key-cards to open locked doors. If you are lucky, the keycard will be close to the lock. And while the levels do wrap around on themselves a lot and the keys have floating indicators, it can mean a fair bit of travel and a greater risk encounter.

After that you start finding rooms with lava filled floors, stationary turrets, and a greater variety of flying machines that can do far more damage to your ship. Each boss core is progressively harder to beat. In a giant crystal cave was the last one I encountered, it was shielded and spinning heavy hitting lasers around while enemy ships and turrets fired at me. This took several runs to defeat. And I died a couple of rooms later on the next level.

As you progress, you can pick up different primary and secondary weapons. All of these have an ammo limit too, requiring you to switch them in and out based on what you have in your reserves. There are 6 different classes of each primary and secondary weapons, with several in each class.

Crafting comes into play and allows you to combine them into new weapon types. These retain advantages and disadvantages of the two that would be used to craft it and are generally more powerful overall. More crafting recipes appear to be unlocked as you play and at the end of each run. This helps to allow the player to slowly get better through a RNG rather than outright skill.

You are limited to a cargo hold space and can only keep so many at once. Eventually having to decide to drop something to get something new, crafting two items to make space, or simply moving on without it. Health Repair pods also take up space and are not activated when you roll over them. Thankfully as with the weapons, you can sit near them and activate if you are low on HP and don't have time to wait or don't have the space to carry them.

They're all listed as in hold and there are no tetris inventory issues in the game, but the large collection of stuff you can find and collect will make you consider what you want to have. Unlike credits or ammo, weapons and health pods do not have a time-out on map, and you can go back and collect them as long as you stay in the same level.

Finally, if you meet certain requirements you can also unlock different ships to start with. I never managed any of these but was able to switch to new hulls while in the individual runs.

My overall opinions are a bit mixed. The game does get difficult really quickly, and each level feels punishing. It is a good type of punishing and I could slowly feel myself getting better without any major difficulty wall.
Sure some areas took longer to figure out than others, but the difficulty curve is a nice 45' diagonal line. Game runs are short, and you can drop out and continue from the start of a level if you ever need to take a break. Otherwise death is permanent and you must start again (with your potential new crafting abilities).

Graphically it is also very pretty and while simplistic at times has a great use of colour and enemy silhouettes are generally easy to tell apart.

If you're looking for something difficult and different in a 6DOF, and enjoy concepts of Rogue-lites I can highly recommend it. But do not go into this game expecting it to be easy for anyone but the pros at 6DOF. And boasting arseholes who think they're so better than anyone else because they're some kind of savant and/or live in a basement playing games for the majority of their waking hours.

Game Acquisition: Purchased at release
Platform Used: GOG
Tweet Thread: 1 - 13 October 2015
PC Used: Scorptec Venom 2009

OS: Win XP / Win 7 / Win 8 / Win 10
Processor: 2.5 GHz Dual Core Processor
Memory: 2 GB RAM
Graphics: Shader Model 3 compliant graphics cards (GeForce GT 520/Radeon HD 3850 and above)
DirectX: Version 9.0c
Storage: 800 MB available space
Sound Card: DirectX 9.0c compatible.