The previous Stealth Inc. – or, to give its original, better title, Stealth Bastard – was a simple game about sneaking, Splinter Cell-style, around a facility full of robots, lasers, laser-wielding robots, and other things put there to make you dead.

The difference, compared to most stealth games, is that you were sneaking against the clock, moving from shadow to shadow and from handhold to handhold quickly and to achieve a reasonable score. There was a heavy puzzle element, but a certain purity to its level-after-level approach that recalled the likes of N and Super Meat Boy.

Stealth Inc. 2, like many a sequel, has decided to expand the concept, stretching a simple platformer into a pseudo-metroidvania featuring gadgets, an explorable hub world and unlockable costumes. The bulk of the game still involves clearing devious test stages, while being taunted by a jerky scientist, but each smattering of levels is now themed around a particular piece of equipment (minus the first, which is more of an introduction).

The original freeware game gave your little bald clone only a pair of light-detecting goggles, but A Game of Clones supplements those with a portable, chuckable totem pole, useful for weighting switches or casting shadows. It's joined by devices that let you take control of enemies, summon a copycat, or illuminate your occasionally gloomy surroundings. There's a multi-stage gauntlet designed to teach, and make use of, each gadget, and after you've passed the relevant tests you're allowed to smuggle them into the hub world to progress or sniff for secrets.

Like the equipment in Zelda or Metroid, Stealth Inc. 2's gear opens up areas that previously seemed impassable, collectibles formerly tantalisingly out of reach. Much brainwork is required to make use of gadgets at times, but when your reward for exploration is another pointless hat unrelated to the theme of the game, you're not exactly being rewarded for your efforts. Compare that punk or cop outfit you just found to a yummy heart piece in Zelda, or a helpful missile capsule in Metroid – these are collectibles for collectibles' sake, and they feel like worthless filler.

Growing up, we longed for open platforming worlds packed with loose ends and secrets, but bigger isn't necessarily better. Stealth Inc. 2's hub area, a testing facility, bears a confusing layout that makes it tough to chart your progress, given how frequently you're shunted around by unseen hands. There's some strong puzzling squirreled away in this main facility, but it never starts to feel like a location, like a place you might want to explore.

Thankfully, the game regains its focus once you step into the discreet test chambers. You can almost hear the developers cackling as you embark upon these challenges, which ask you to reach the exit in the shortest time possible, and with a respectable number of deaths. Merely hitting the end is something to celebrate later in the adventure, when there are all manner of devilish enemies, traps and obstacles lying in wait. Generous checkpointing helps to limit frustration, but it's not entirely eliminated thanks to the odd section that prioritises trial-and-error over player smarts or skill. Restarts are, blessedly, instant – but deaths should always be our fault, and it doesn't always feel that way here.

Frustration is part-and-parcel with games that truly test you, however, and we wouldn't want to give up one for the sake of the other. Like the best puzzlers, Stealth Inc. 2 makes full use of its mechanics, gently teaching players how to use them even as it wrings its high-tech doodads for all they're worth. Something was lost when Curve decided to embiggen the wonderfully lean original, but the marrow of this sprawling platformer is very much worth digging into.