When a studio has a surprise hit such as SteamWorld Dig, it would likely be forgiven if a straightforward sequel rapidly followed. That doesn't seem to be the norm on the eShop, however, and Image & Form has produced an ambitious follow-up in the form of a turn-based strategy game with a twist, placing trick shots and shooting accuracy front and centre. Though SteamWorld Heist buries itself in more complexity than its predecessor, carefully crafted systems and the charms of the IP combine for another excellent portable experience.

Arriving on the 3DS first, in honour of the importance of the system in Dig's breakthrough, Heist is an excellent fit for the platform. Many 3DS owners will be familiar with turn-based strategic gameplay, meaning that even with its own approach to the genre Heist feels at home on the portable.

The core gameplay loop involves a team of steambots, from solo battlers to teams of four, taking on a host of stages that each form varying challenges. The perspective is locked on a 2D side-on angle, with caters to the skill-based combat system at play; though much of the usual strategy ideas are here, such as managing a team and positioning your crew carefully, the manual attacks serve to add a new layer of pressure to proceedings.

As a system it's certainly fresh, and undoubtedly addictive. At times we've set up the scenario well only to make a bad mistake and miss with an easy shot, while some of our most memorable moments have been pulling off unlikely distance or trick shots when our backs were to the wall. As a result it's a smart gameplay mechanic - though statistics such as your attack power, enemy health and so on still matter, a moment of outrageous skill can tilt a battle at a critical point. It's effective at adding tension to the scenario and, in a particularly deadly way, enforcing a 'one-more-go' mentality that can see multiple hours pass by in a single sitting.

Combined with carefully crafted balancing, which we'll address more further on, this system works wonderfully. After a brief tutorial it feels natural to move with the D-Pad, either a little to then complete an action or shoot, or perhaps to 'sprint' further and sacrifice a shot or item use. Taking cover is also integral, while explosive barrels and more complex environmental aspects later in the game give more to ponder. On the one hand all of these factors combine to deliver a fairly substantial set of mechanics, and on the other it's very simple and easy to understand when actually playing.

One point we've noticed in general play, however, is that the visible real estate on screen is relatively limited - which will likely broaden and zoom out in the HD Wii U version, as happened with SteamWorld Dig. This can be worked around with Circle Pad camera movement, meaning the occasional need for 'longshots' where you cross your fingers and hope for the best. Our only minor criticism of the overall combat system, meanwhile, is that learning enemy unit move distances is trial and error; you can't select an enemy, for example, and assess their movement and attack range. Fairly aggressive tactics can overcome this, while adopting cover and strategically utilising solid walls and floors - rather than those that can be shot through - provide the means to ultimately plan for the enemy's attack.

Your robots and the varied enemy bots you face all fit into loose classes and types. On a basic level this affects the kinds of guns they can operate, from pistols to grenade launchers, shotguns to long distance sniper-style attacks; you start off with just two crew members and recruit more on a fairly linear basis. The pacing is excellent, in that you generally get introduced to new compatriots once you've begun to master the existing team, which helps to maintain a sense of momentum to the campaign.

Beyond basic weapons each has their own special moves and buffs to offer, which later in the game allowed us to settle on a core team that matched our preferred style. Completing levels shares experience points among the bots you took on the heist, and the volume of XP varies depending on performance. Each stage has three stars to earn - two for objectives and one for picking up the 'epic swag' item - while each lost crew member deducts a star. Any robots shot to pieces in battle do return on your hub ship, but the lost character does lose its share of earned experience points.

Gaining experience is truly vital, too. Levelling up a character unlocks a mix of improved stats such as health or, more usefully, new abilities. Varying your crews early on to see how each character levels up is a key tactic, and also fun, and as you approach the close of the campaign your strategies will be unrecognisable from the start. Perhaps you'll be utilising movement to flank enemies more, trying to gamble and initiate powerful melee attacks, or seeking all-rounders that can survive the toughest encounters.

All of these strategies matter, especially as enemies become more diverse and tricky to handle, while Boss encounters are also particularly challenging. These take a lot of hits to put down and are most likely to necessitate level restarts, especially in the closing third of the story. Some bosses are brutes that simply chase you down for powerful melee strikes, while a particularly memorable foe pulls off outrageous ricochet shots.

If the going gets too tough you can alternate between five difficulty settings at will when you start each mission. This is particularly handy in terms of strategy or if you're stuck and simply want to make some progress. In the easiest difficulties there are no extras or penalties, but once you opt for the third setting and up you gain more experience points for successes and, crucially, failed missions will take a percentage of your overall pot of money. That's some serious risk-reward, especially if you've saved money up for a particular item; when we had a pot of cash saved up we occasionally backed down a difficulty level, though some players will undoubtedly be braver.

Overall the structure of the gameplay, with the combination of 2D turn-based strategy with manual attacks, works wonderfully. It's a hook that works so well courtesy of the diversity of guns and attack types, and in addition there are lots of inventory items to acquire or buy. The constant looting of ships when completing missions keeps you in the money and swapping out items, with limited inventory space emphasizing prioritisation. There's a nice balance of depth and simplicity; there's plenty to consider, but it's managed and limited to ensure you're not overwhelmed.

Contributing to all of these mechanics, thankfully, is a similar degree of design charm as was so vital in SteamWorld Dig. The setting of robot clans traversing space sets up some humorous narrative points, from the questionable motives of the Scrappers, to pompous and dangerous Royalists and more besides. The cast of playable characters, enemies and NPCs that populate the bars and shops is quirky and diverse, with some fun writing bringing them to life. There's also the silly meta game where you can shoot the hats off enemies' heads during battle, if you're feeling bold and want to shake up your collection. Utterly silly yet, at the same time, impossible to ignore when you want your crew to look that bit more stylish.

Strong presentation values are at the heart of SteamWorld Heist, too. Visually it does a fantastic job with the steampunk aesthetic, at times portraying grubby and clunky metal and at other points showing a little more splendour or surreal design. The image also has an extra sharpness and clarity, to our eye, once the 3D effect is enabled; it's a subtle effect but adds some welcome pop. There are stylish cinematics too, mimicking old-school information broadcasts that bring to mind 1930s UK cinema reels, right down to the dramatic orchestrated music.

A mention should also go to the soundtrack. General stages have pleasant, atmospheric music that does its job well, but a favourite touch of ours are the tracks by real-world band Steam Powered Giraffe, who appear in-game as bar performers. Combined with the strong sense of style and technical accomplishment of the visuals, the soundtrack contributes in a notable way to the overall vibe when playing.

A final point to address is the game length, naturally. With a higher price than its predecessor the focus is not only on the different gameplay style, but how much value it offers. The core campaign is rather lengthy, thankfully; we blasted through it in about 13 hours, albeit while dropping the difficulty on multiple occasions to smooth out our progress and skipping a couple of optional 'Challenge' stages. Most players will likely add a couple of hours to a normal first playthrough, and there is a neat - albeit modest - twist in a New Game+ option. We're certainly keen to play through again using this + mode while shooting for full completion, but even for those that don't have the same urge it's a meaty story on offer.