A quick comparison:
In Katamari Damacy, each level is filled with stuff. Collect X amount of stuff in Y minutes. As you collect more stuff, your ability to collect larger stuff increases.
In Elebits, each level is filled with stuff. Elebits hide behind/in the stuff. Collect X amount of elebits in Y minutes. As you collect elebits, you are occasionally rewarded with a chance to collect special elebits. As you collect the special elebits, your ability to move larger items of stuff increases.
So you can see that the basic idea is the same in both. Start out collecting the easy stuff, as you grow in ability you go back over the same areas collecting stuff you couldn't collect before. The ways Elebits has changed the game, though, are what make it a must-have. For one, PHYSICS is here! Is there something too large for you to move? Then grab something slightly less massive and fling it really fast at the larger thing. The larger thing will budge a little, perhaps enough for you to get where you need to be. :) Also, the elebits will react to you. Some don't want to be captured and will run if you come near them. In KD, the stuff you were trying to collect was largely unaware of you so it was no biggie if you missed on the first try, but now you have to collect them quickly before they run off and hide under the lamp you tossed aside previously. Oh, and speaking of lamps, some are breakable. As are other things on the levels. Once you hit level four it introduces the concept of a breakage limit. In levels one through three, you were wildly tossing stuff aside and generally wreaking much havoc as you went. Now you have to be more careful. Can't just toss that chair to the side as it might slam into that piece of china on the shelf and break it. And once you've broken beyond the limit the level is failed. There's also some other level restriction that I don't know what it is yet. The game slowly eases you into the restrictions and challenges as you work up the levels, which is a good thing since it can take a little getting used to due to the controller.
Oh, yeah, and about the controller. Where in Zelda it's just a poor port of a traditional controller and in MonkeyBalls it's sensitivity is annoyingly inconsistent, in Elebits the controls are natural, consistent and smooth. They use it in ways that I don't think you could possibly manage with a traditional controller. For example, you can grab a boot from across the room and lift it up while at the same time pulling it towards you and tipping it over while shaking it so any elebits inside will fall out in the middle of the room closer to you, all the while you are walking out from behind a desk and moving to get a clear shot at those little 'bits if they do fall out of it. Let's pause a minute and think about the amount of controls needed here. There's the one analog stick for your movement, okay. There's another for the moving the boot up/down/left/right, okay. Then you've got something that will move the boot towards/away from you, let's say those would be your R1/R2 buttons. then there's the tipping the boot over, hrmm, L1/L2 perhaps? Then there's the actual firing of the gun that grabs the boot in the first place (you have to hold this one down), so that's A. But you're hold it down while you move the right analogue stick -- good luck with that one. Plus there's also the shaking the boot, guess that has to be B. And did I mention you could be doing all this while stretching up over the desk or crouching from under it? Okay, those would be two other buttons you need access to. To have done all this on a classic PS2 or GameCube controller would be awkward at best, if not downright impossible. Yet with the Wii, it's done using only one button on the WiiMote for firing (you pick which one works best for you, trigger or main), the buttons on the 'chuck (crouch/stretch) and the one analogue stick (motion), with the WiiMote's motion sensing taking the rest. And it all feels so perfect once you get used to it that it's like you are actually reaching into the game.
And a word about "once you get used to it". The game has a tutorial mode that it prompts you if you wish to use before you get started. And once you've played a few levels it again asks if you'd like to see the tutorial before it introduces a new gameplay concept. So the learning curve is very well managed. Not that there's much of a curve in the first place; I was having fun playing it within ten minutes (it felt more like five, but I wasn't timing) of loading the game and I haven't yet even glanced at the manual (I'm assuming it comes with one, didn't check yet).
In summary, Elebits is the first game that I've felt good about getting for the Wii. It is playful and fun with its style and approach. Each level goes quickly enough that you don't have time to get frustrated if you can't figure something out, you just start over and try a different way. It saves between each level so there's never a problem of "don't have time to play right now, have to be leaving in 20 miunutes". The controls work perfectly. I am very happy with it so far. Only problem I can see there being is a possible lack of levels. They did think about some of that, though in that each level, once completed, can be edited and special challenges can be created. Plus, it will go online and let you trade homemade levels with your friends (don't know how this works, still haven't gotten my Wii online yet).
Where previously I ranked MonkeyBall and Zelda at 3 and 4, respectively, and Wii Sports at a 6, I feel Elebits is easily a 7.5 or 8. Not good enough to skip work to play, but I have planned on playing it all day today (with perhaps a little break 'round lunch to work on getting some desert pictures up here for y'all). I'm very pleased with it and this makes me feel much better about the Wii overall (was getting worried, since the real success of a console lies in the games that come out for it, and two of my earlier experiences were not very good at all.).