I have not played it, but from Metacritic...
100Play Magazine
For someone who feeds off of the connection between game and player, the kind of connection that only the very best can forge, an hour of Wario is worth ten of a game that only pays of sporadically. Wario World pays off every second I'm holding the controller, and that, to me, is greatness. [June 2003, p.60]
90Deeko
Weighing in at 6-10 hours, the game is short. However, veteran gamers will enjoy coming back to Wario World time and time again for the great graphics, sound and gameplay.
85Game Informer
No Treasure game would be complete if it wasn't replete with awesome boss battles. Wario World has them in droves. [July 2003, p.108]
85Nintendojo
In spite of its shortcomings, Wario World is a fun throwback to the simpler games of the 16-bit era and is most certainly worthy of the Wario name.
80Nintendo Power
Although WW is not very deep, it is tons of fun. The challenges are tricky at times but rarely frustrating. [July 2003, p.80]
80GameShark
Nintendo fans will jump all over this but Treasure fans and casual game players may just want to rent this one out.
80GameCube Europe
You’ll have a great time playing Wario World without any doubt, but it’ll be over before you want it to be. If you don’t want to spend money on short games, try to rent or borrow Wario World, it’s really worth playing.
80GamePro
In an age when platformers are searching for the next gimmick, Wario World stays addictive by weight of sheer design innovation. Shame it’s so short.
80Armchair Empire
A fun, splashy, albeit short and easy game with some great small touches and a hint of sidescrolling nostalgia.
76netjak
Wario World has many of the same qualities as its protagonist. It’s slightly rotten but likable, a bit too short, and awfully greedy.
75Firing Squad
Even though the entire concept and execution is far from original, everything was well done...It's tough not to like a game that's just so delightfully evil -- pity that it's over all too quickly.
75GameNow
My biggest beef with Wario World is that it's over too quickly... If you love looking for secrets, though, Wario World is a great diversion. [July 2003, p.47]
71IGN
Like "Luigi's Mansion," what's there is good. I just wish there was more of it.
70Cincinnati Enquirer
WW isn't the best platform game on the console, but it has its charm.
70EuroGamer
Where the game falls down is its length; at around eight hours it's going to take you less than a good weekend session to plough through it, and for £40, frankly that's not good enough. It's "Luigi's Mansion" all over again.
70GameSpy
For the most part, Wario World offers little above and beyond the standard 3D platform romp, and what is offered turns out to be very short and repetitive. That's not too say that the game isn't fun while it lasts, because it is -- I just wish there was four times as much to crack.
70GMR Magazine
It's a fun, imaginative platformer that, though easily and quickly completed, is another solid first-party GameCube title. [July 2003, p.74]
68Electronic Gaming Monthly
The levels are tight, fast, and fun - less about aimless exploration and more about reflex-testing action. But on the other hand, I'm a little disappointed that it's so short and simplistic, and that it doesn't take more advantage of the GC's hardware. [July 2003, p.114]
67Game Revolution
Equally goofy and strange, but in an unassuming way, it's also good, unpretentious fun.
65Nintendophiles
It's not bad, it's just too short and without enough substance.
64GameSpot
The game certainly contains a lot of the same Wario charm that makes his GBA appearances so memorable, but the final product is too short and simplistic to hold your attention for more than a day.
60Gamestyle
No-one was expecting a heavy, lengthy platformer, but neither the puzzly-jumping nor the fighting has been nurtured enough to shine through, and as it stands Wario World is a missed opportunity; not particularly bad, but certainly not what we'd expect from two of the finest developers in Japan.
60Yahoo! Games
No lines are crossed and no boundaries are broken. Good stuff, but still stuff you've seen many times before.
60G4 TV
The fundamental gameplay is so strong and so well executed. But it's over so fast without enough challenge that you can't help but want more. Never before have I found a game that screams rental so loudly.