I guess that most Bollywood movies will strike western viewers as somewhat quirky in terms of storytelling structure and acting, but compared to other Bollywood movies I've seen so far, this one seems to be an exceptionally quirky one.
The story is fairly simple: rich boy (Ajay Devgan) and poor boy (Aamir Khan) are best friends, rich girl (Juhi Chawla) and poor girl (Kajol) are best friends. Rich boy falls in love with poor girl, poor boy falls in love with rich girl, and the two rich fathers will do anything to destroy the two budding relationships.
That's basically it. There is no real plot; instead there's a sequence of scenes where the two fathers devise a dirty scheme, which is promptly thwarted by the young lovers. On to another scheme, which again is not successful. The next dirty plan follows, which... you get the idea.
Still, the evil schemes become increasingly more devious, and their consequences more severe as the film progresses; along with this progression, the film makes its way through all genres that you can imagine: it starts out as a fairly silly slapstick comedy, turns into romantic comedy, then into romance, then into thriller and finally into a tragic melodrama. At one point, there's even a horror scene thrown in for good measure.
Plot holes and illogical character behaviour aplenty, but that's what you expect of any Bollywood movie, more or less.
As for the acting, well, don't expect stellar performances. Most of the supporting cast are somewhat annoying, especially in the slapstick scenes, although Johny Lever for once plays a fairly non-silly, likeable character.
The lead actors give solid performances, particularly Kajol and Aamir Khan, who manage to be funny (without overdoing it) in the comedy bits and believably serious/emotional (without overdoing it) in the tragic parts. Ajay Devgan has great onscreen chemistry with Kajol (they aren't married for no reason, it seems), but overall his character has a serious depth deficit and is just too gullible. Juhi Chawla is very pretty and good fun to watch, and it is her very energetic performance that drives the movie along much of the time. However, she is mostly really more of a pleasant diversion than a full-fledged character.
The music by Anu Malik has no real highlights and, like the film, probes its way around several genres. My personal favourite is 'Dekho Dekho Jaanam', a compellingly cute, slightly silly Kajol/Devgan love duet (sung by Udit Narayan and Alka Yagnik). 'Ishq Hua Kaise Hua', the corresponding Chawla/Khan duet (Udit Narayan/Vibha Sharma) is more romantic, much less successful, but comes at least complete with lots of Swiss Alps. The disco-inspired songs are, alas, not very inspired.
Overall, this is a 3-hour tour de force, an all-in-one package of all emotions and film genres that you can imagine; not really the best of Bollywood, but still fairly enjoyable. Not sure whether it's worth the trip to the cinema, but rent the DVD and watch this if you are in a quirky mood or if you have friends over for an Indian dinner.