The ways in which Thomas Happ's Axiom Verge are similar to the Metroid series seem like an easy justification to dismiss it as a knock off. However, even after playing it for only an hour, it becomes obvious that there's much more to this package than the Metroid game you may never get again. There is an obvious inspiration, that's undeniable with the way it wears it's influences on it's sleeve, but Axiom Verge does enough different to demonstrate why it is it's own thing. The most important thing is, no matter how you feel about it's origins, Axiom Verge is addicting, enthralling, and just all-around delightful.
Waking up in a strange egg-like chamber, you play as Trace, a scientist from Earth who was involved in a lab accident and found himself on what he can only describe as an alien planet. There, he meets Elsenova, one of the Rusalki, now dormant inhabitants of the world of Sudra. With her help and guidance, Trace sets out to find and repair the other Rusalki, stop the looming threat to their world, and find a way back to his own. While there certainly aren't too many ground-breaking ideas at play in the story, I would be remiss if I didn't mention that there is more at play here than just the typical "stranger in a strange land" finding his way home story. The story and dialogue breaks are infrequent enough to not become overbearing, while also not too far apart as to become forgettable, creating a nice balance of something that serves to create intrigue and push forward towards.
Really though, the primary reason you'll likely want to push forward is just the nature of the gameplay itself. Trace starts with only one weapon, the 'Axiom Disruptor', an incredibly basic "shoot one shot in the direction you are facing" weapon, and from there you can find dozens of interesting and unique weapons, including the shotgun-like 'Kilver', electrical web shooting 'Voranj', and the boomerang firing 'Reverse Slicer'. As well as weapons, there are a host of other gadgets required to navigate around Sudra such as a grappling hook, a drill, and a coat that allows for teleportation through thin walls. What Axiom Verge does incredibly well is create a sense of excitement for more exploration every time a new tool or weapon is acquired. The feeling of "oh, now I can reach that ledge from four rooms back" is a real thrill, and each time I got something new, I would make my rounds through the areas I had already explored to look for new goodies, and the basic platforming and shooting is tight enough that this never feels like a chore.
Playing primarily on PlayStation Vita, there are some technical hiccups, but nothing too outrageous. The backing music tracks - which, by the way, are quite good - would sometimes just cease all together until I traveled through a door (and even then, not always). More jarring, however, are the occasional freezes. These were never so distracting as to be frustrating, or to cause a cheap death, but they did happen roughly every fifteen or twenty minutes for a second.
Those issues aside, there really aren't any glaring complaints to make about what's offered in Axiom Verge. It may seem like a budget Metroid clone because of it's visuals, sound design, and 2-D side scrolling nature, but the vast roster of colourful weapons and items, as well as the way you interact with them, has more in common with Ratchet & Clank than it does anything else. The joy of it's careful difficulty curve and continuous drip of new abilities makes exploring feel more fun than it does a necessary function of furthering the action, and at a length of around ten to eleven hours to complete, it doesn't overstay it's welcome while also feeling pretty substantial. It took a long time to get here, but Axiom Verge is absolutely worth it, and leaves a fantastic lasting impression.
(Edit - I initially gave Ophelia as the first Rusalki you meet, when in fact it's Elsenova.)