In terms of difficulty level and structure, I think Square-Enix has got the balance spot on. Hardcore, score-attack obsessives get a mode where save points and continues are outlawed and all scores are uploaded via the Nintendo Wi-Fi Connection to a central leaderboard. The rest of us get a more generous arcade mode where the game saves after each boss battle and you can retry the level as much as you like. The result is a game that's horrendously addictive, but one you can still play in relatively bite-sized chunks. Unlike some other recent retro blasters, nobody is forcing you to play and replay the same stages over and over and over if you don't want to.
The one weakness is the multiplayer option. Square-Enix gets points for including download play to a DS without a cartridge, plus online play over WFC, but the actual multiplayer offering is a pale shadow of the single-player game. Basically, two players face wave after wave of aliens until one loses all their lives. Shooting the aliens creates a store of grumpy invaders, and blasting a mothership unleashes that store upon your opponent. It's OK, but a little bit dull, and it really just leaves you champing to get back to the main game.
This isn't the most revolutionary DS game of the year, and I have my doubts about its long-term lifespan, but given the low street price (you can easily get it for less than £15) Space Invaders Extreme is perfect for a quick blast in the sun, a little distraction on holiday or some serious time wasting while you're travelling. The key test for me - and this applies to any portable game of this ilk - is whether I find myself sneaking goes in when I really should be doing something more important. It's a test that Space Invaders Extreme passes with flying colours. Hours have been mislaid in the bathroom, or in my home office while I was 'just checking mail' and in the garden when I was supposed to be watering the tomatoes. That might not be good for productivity or family relations, but - damn it - it's good for the soul.
A storming retro reworking that actually works! Space Invaders isn't the deepest or most innovative DS game of the moment, but it looks good, sounds great and proves horribly addictive.