I expect the standard thing to do here is to remark that Yoshi's Island was the most astounding, mesmerising, stunningly inventive 2D platform game of its generation, and then go on to talk about how Yoshi's Island DS does the same things with a few more additions and is therefore also excellent.
But I don't really feel that way, and I suppose it's because a sequel to Yoshi's Island is self-defeating. The first one was, in effect, Super Mario World 2, and it was made at a time when Nintendo still understood that to truly improve on something of that game's incredible significance meant ripping it up completely, and proceeding with only the most fundamental elements intact: in Yoshi's case, the controls, and the collectibles. Of course, back in 1995 they were doing this on two fronts, with Super Mario 64's development running parallel.
Artoon's attempt to rework Yoshi as a DS title doesn't do this. You're looking in the wrong place if you're after a DS platformer that has the SNES Yoshi's determination to use the technology - without being brash about it - to create brilliant new scenarios, and new experiences that turn convention on its head (or rather, get it drunk, pull its trousers down, and generally fart all over it). For that, you're better off looking to New Super Mario Bros., which comes closer even if it doesn't get there either. This is like a distended version of Yoshi, and its appeal is ultimately a bit limited.
That's not to say Artoon hasn't worked hard to fill out the DS game, mind you. Yoshi retains his usual abilities (running, jumping, hovering with well-timed B-button flutters, converting enemies into eggs and firing them using an aiming cursor, and of course bouncing on heads), but this time it's not just Mario and Luigi he and the rest of the Yoshi clan are worried about. There are now five babies, with Yoshi carrying one at any given time, and able to swap it over for another at special "stork points", where his beaky companion offers him a choice of baby Peach, Donkey Kong, Bowser and Wario depending on how far you've gone.
The benefit of swapping babies is that each augments Yoshi's basic skills with one or two of their own. Mario allows Yoshi to dash (useful on disintegrating platforms), while egg projectiles fired while he's onboard will bounce off walls, allowing you to tag far off collectible flowers and cloud-blocks to help reach new areas. Peach can hold out her umbrella to help you float upward on gusts of wind, while DK's explosive eggs are only part of his appeal - unlocking as he does the ability to clamber along vines and chains, swing from hanging ropes and shoulder-charge through walls. I don't want to spoil everything, but let's say Bowser and Wario also have a sort of fiery magnetism to them.
The game is still split into eight stages set across five different worlds, with a pair of boss castles for each, unlockable extra levels and mini-games to find too. Individually the levels are much bigger, with greater complexity brought about through the addition of new types of collectible (like the Big Golden Coin, and red coins hidden among all the regular ones), and the constituent parts of each are certainly diverse enough to sustain their girth. No one can claim Yoshi's Island DS isn't varied. There are pressure-switch platforms that you can stand on as long as you want, but which will only bear your weight a certain number of times; there are competing wind currents to ride; there are circular moving platforms with arrows on them that continually spin and follow the direction they're pointing whenever you're standing on them; there are Yoshi's traditional vehicle morphs like the mole and helicopter, and a new bouncing kangaroo; there are swinging bits and flapping bits and swollen others, and really every flavour of platform imaginable.
Principally it's all about getting to the end and leaping through the flowery goal to pass your current baby to the next Yoshi in line, but of course that's barely half of it - with the real challenge coming from scouring the level for coins, flowers and mini-game doorways. The tantalising sight of a door you can't reach or a flower that's beyond your grasp is the closest thing the platform genre has to Zelda's perpetual hook, and Artoon's new concepts are used to help amplify the effect - with certain collectibles plainly within reach of a particular baby (Mario, for example, whose presence turns useless outlines into solid "M" blocks). The use of both screens, too, means you can look further afar for things to acquire - and the decision to acknowledge the gap between the DS' two screens, rather than pretending it isn't there, means that aiming always makes sense to your brain, avoiding the pitfalls of games like Bubble Bobble Revolution.
But then Artoon takes things a bit too far. It hides things in the gap between screens, which is, I suppose, a clever acknowledgement of the fourth wall, but at the same time it also means you're constantly looking up and down to make sure you've not missed anything. You have the ability to switch Yoshi between top and bottom screens to see what's lurking above or below him, but relying upon it to make up for the designer's conceitedness does it no favours.
There's a similar feel to the baby-swapping idea - it's clearly there to encourage replay value (when you get DK, your first reaction is to think, "gosh, where have I see those vines before?"), but the process then becomes backtracking and not exploring. Yoshi's original charm wasn't just that completing each level to 100 percent was satisfying, it was that you knew the developers were off-screen squeezing surprises into every last secret pixel. You trusted them. They were there to make sure you had fun. Artoon clearly wants to play that role, but ends up creating doubt with some of its design decisions - the trust isn't there, and instead you're constantly wasting time casting about to make sure they're not trying to trick you again.
There's certainly great depth to what's been achieved, and like New Super Mario Bros. it's not a mean-spirited game. It does get very tricky later on, but you always have far more lives than you really need, and the traditional system of having Yoshi drop his baby and have to pick it up again within a time limit, rather than simply dying if he brushes too many enemies, means that losing masses of progress is relatively rare. That's also helped by nicely spaced save points, which sensibly also checkpoint you just before boss battles.
But really it all comes back to the fact that Yoshi's Island was doing almost everything for the first time, and Artoon is cribbing from the same notes. It's a shame, because there are times when you catch glimpses of the sort of thing the Japanese team is really capable of - like a ghost boss in the second world who is invisible on the top screen, and has to be tackled by using an upside-down reflection in the touch-screen to judge his position. With each strike, he cracks the mirror to make things more difficult. When Yoshi's Island DS does things like this, you smile. It's compelling.
The problem is that it's a sensation that you felt all the time in Yoshi's Island. You gave up counting the ways. Counting them here would result in a much smaller number, like, ooh...