There was a period where I couldn't go a week without a shooter of some variety to gush about or strip down; while trends like this are to be expected, it sorely tested my interest in the genre. What makes it odd is the distinct void that I hadn't anticipated from having not played a shooter in a long time and the idea of Boss Battle's free abstract boss-fighting gameplay was like an oasis in a vast, dry desert.

One should caveat the whole 'free' thing before moving on though; for those familiar with Backflip Studios you'll recognize their method of extracting payment from their customers through obtrusive banner advertisements slathered over the top of the screen. IAP for additional gems are also available, though no ad-free option seems to be on the cards.

These gems are used as upgrade tokens and are exchanged for permanent unlocks and upgrades for weapons and 'pods'. You'll need to make the most of these gems as each boss has a particular weakness (almost Megaman style) that makes taking it out a snap - relatively speaking. See, killing a boss will initially only unlock the next in a series of eight stages filled with a wave of minions followed by a tense boss battle (hence the eponymous title). This only annoys the creature and the next time you attempt to kill it (for an increased bounty) the boss will sport a few new tricks (often amounting to increasingly complex minions and more bullets).

Sadly there's no real challenge to the bosses as the patterns are simplistic - a thing you'll be grateful for as keeping track of the small purple bullets can be a pain, especially when your ship's hit-box is so large. Once you've picked up on the optimal weapon setup and attack strategy you'll be laughing all the way to the bank.

Boss Battles makes its case almost entirely off the back of its free price-point - something some gamers will no doubt appreciate, but a minimal investment opens up the door to a host of far deeper abstract shooter experiences. A decent budget title for the shooter fan with spare time.