You'll probably need to do this just to progress at first. The new Beginner mode allows you to play the easiest route through the game with infinite lives; it's a welcome way to learn Extreme 2's systems for new players, but it does train you to think about the game's mechanics first and simple survival second. Going back to a limited stock of lives in normal mode is a rude awakening. In fact the game is generous enough, only resetting multipliers when you die and putting you back to the start of stages (with your score saved) when you lose all your lives. But you're so lost in trying to construct Bingos that you forget to dodge bullets.
Bingo Fever is an ultra-high-score Fever Time, in which you can shoot down pink UFOs for massive point payouts. You get it by lighting up three squares in a row on the three-by-three Bingo Panel on the top screen, each one representing one of the nine permutations of colour features you can get (four red Invaders followed by four blue, four blue by four green, etc.). You also get Two Lines Fever and Full House Fever for completing two or three rows at once. Features are easier to get in Extreme 2 - you only need to worry about colour, not shape - which together with the introduction of Bingo shifts the game subtly from skill and luck towards planning and puzzle-solving.
It's also completely irresistible. There are plenty of other escalating satisfactions in Extreme 2, from the simple chain that unleashes the 16x Break mode when it passes 100, to the cannon levelling, the game-changing effects of Features using the black Invaders and more. But bingo becomes an obsession to the point of willingly making things harder for yourself, subverting the basic mechanics - survive and keep killing - of the shmup. That's great game design.
The other principle change to the game flow in Extreme 2 is the use of the DS' top screen. Rounds, usually requiring you to shoot down outsize Invaders with strange behaviours, now take place in the top screen, with the waves of Invaders progressing as normal below. This is a great twist, turning the somewhat basic and showy Rounds from an interruption to an addition, and requiring some acute visual awareness. Boss battles, too, fill both screens to great effect, and they're even more witty and surprising than they were in the first game.
Extreme 2 has decent multiplayer features; there's a return of the local and online versus mode, with new ways to send waves and UFOs over to your opponent's game which appears in the top screen. There are online leaderboards too, tracking scores in the harsh Ranking variations of Time and Score attack which don't allow continues. It's great to see these in a portable arcade game, even if they do make you pine for the home consoles' friends lists.
It's also a shame that there aren't individual scoreboards for the Stage Select mode, which allows you to perfect individual stages in both Score and Time Attack. Extreme 2 is relatively long from beginning to end, and Stage Select is a great option for short-haul perfectionists, so it's a pity not to be able to share your achievements here.
Space Invaders Extreme 2 is more balanced and involving than its predecessor. Its intricate combo scoring is more accessible, deeper and more addictive than the first game's, and it has plenty of longevity - there's an Extreme difficulty with all-new patterns and Invader types, unlocked by completing all branching levels on Normal - even if you don't get into the faintly unsatisfying Time Attack. But it's more of a perfected version of the first game than a true sequel, so it's mainly diehard fans and the uninitiated who should be descending on their game shop for a copy.