My first introduction to Aishwarya Rai (in her first major Bollywood hit), 'Hum Dil De Chuke Sanam' excels at presenting fantastic dance set pieces and songs, as do most successful Indian films. While the pacing can drag at times (as is also the case with a lot of Indian films), most issues are saved by the Rai's charisma and the aforementioned musical performances.
Where HDDCS really stumbles is in its dialogue. I've said it before and I'll say it again: Bollywood actors' tendency to overact and drown in melodrama can really bite their movie in the ass when the script isn't focused on the dance scenes. I'm not suggesting melodrama or passionate acting are inherently bad, rather, I'm simply saying that any missteps that occur when engaging in this type of acting are felt particularly hard by the audience.
As I hinted earlier, a common type of misstep is awkward dialogue. Overacting and melodrama, if not used appropriately, can absolutely kill dialogue and turn a movie into a painful mess. I thought Salaman Khan was incredibly annoying in this film because of this. Furthermore, Bollywood melodrama and overacting (as is perfectly exemplified by this film) has other problems that go behind the awkwardness that can ensue. A little bit goes a long way, and pacing can be affected. This is the cause for the dragging in this movie (other than the 3 hour+ run time). But I digress.
The second half of HDDCS is a lot stronger than its first, and most of the pacing and dialogue problems are handled more effectively. Ajay Devgan's more subdued performance also elevates the movie's latter half, and he is far more likable than Khan. I found the justice done to him at the end of the movie was great, and concluded the story well.
In the end, HDDCS's performances from Rai and Devgan and the mesmerizing dance/song scenes outshine its weaker points. HDDCS, in giving credit where credit is due, is a real treat for choreography, music, and costume design. Well worth your 3 hours and 7 minutes ;)