So far, no game with "PixelJunk" in the title has made any serious missteps. Until now, none had a full-fledged sequel, either. Previous PixelJunk games have had their "Encore" updates, adding a good amount of extra content to already-admirable downloadable games. This time around, instead of merely releasing an expansion pack, Q Games has made a standalone sequel.

The original PixelJunk Shooter was an interesting concept. It's a 2D twin-stick shooter, set on an alien planet. Instead of being a combat-focused game, though, it was almost entirely based around physics puzzles, mostly relying on some excellent implementation of fluid dynamics. Enemies were few and far between, and boss fights were more about manipulating the environment and proper timing than just blasting away.

The focus on puzzles has remained for the sequel, and has been ramped up a few notches. This time there's more combat, although it has been incorporated into the puzzle sections beautifully. The darkened areas are particularly impressive, where attracting attention from certain enemies is necessary to light your way, and to avoid the attention of even nastier shadow-bound threats.

The interplay between darkness and light is new to the sequel, and it's used in an interesting way. Simply moving into the shadows leaves you vulnerable - you can't grapple the scientists you have to save when they're in shadows, and enemies in the shadows are only visible from very short range. But more importantly, being in the darkness spawns dozens of eye-creatures, which slowly drift towards you, then dash in one by one and latch on.

While you remain in the shadows, they're invulnerable, so you can only remove them by performing a spin attack once you're in the light. As long as you have even one of these things attached, your heat gauge will constantly rise, until your ship overheats and crashes. There are other enemies which can only attack when they're in the darkness, and will retreat from light sources. Being forced into the light doesn't kill enemies like this, but it does render them vulnerable to attack.

The problem with Shooter 2 as a standalone game has nothing to do with the volume of content. It's not even about how much of the content is new – the game offers plenty of upgrades and new challenges, and even the old elements take on new roles because of it. The fatal flaw is actually part of what makes it so much fun. It's too hard for an average gamer to just pick up and play, unless they already finished the original. The boss fights are particularly brutal, but there are many challenging moments outside these sequences as well.

Some will force you to think outside the box, others simply require you to move with precision beyond many casual gamers' patience levels. Fortunately, the lives the game counts are those of the civilians you have to rescue – should five of them die, you’ll lose. On the other hand, your ship can be obliterated over and again without any real penalty – you’re just reset to the entrance of the area. There are plenty of these checkpoints scattered through normal levels, but, frustratingly, the boss fights don't have any. They require perfection all the way through. Nonetheless, succeeding at these challenges comes with a great sense of satisfaction and makes the effort worthwhile.

The art style and music are much like the first game, and both help to set the tone for the game - not too serious, but clearly requiring quick thinking as well as fast hands on the controls. The simplistic graphics understate the physics applied to the environments, oddly helping to make the world feel more real than it would with more detailed visuals.

Making sure the behaviours of all the different materials is unique, and their interaction with one another is consistent and understandable, is by far the highest priority, and the attention to detail here is amazing. When you first encounter a new substance, you'll want to experiment a little to work out how it behaves, what happens when you shoot it, and when you mix it with lava, water, or anything else nearby.

One of the most important new features in Shooter 2 is the online multiplayer. It adds yet another layer to the game, challenging players competitively, in addition to the original's single-system co-op. Finding a random opponent online can take a while, and challenging friends doesn't help you to unlock the abilities you'll need to compete effectively. Co-op mode is as fun as ever, whether you're working together efficiently or laughing at one another's repeated deaths.

The challenge may be a little steep for newcomers, but PixelJunk Shooter 2 still lives up to the standard of quality and fun Q Games has consistently delivered.