I played BDSP (Shining Pearl), then I played Platinum after it. And BDSP is just the better game, in my opinion.

I will admit, Platinum has 3 things over BDSP:
>the Battle Frontier
>the better Plot (with Distortion World, Looker and Charon)
>the Villa

But everything else is better in BDSP:
>The Grand Underground is much bigger and better designed than DPPt's Underground
>Super Contests are simplified and actually fun, unlike the original Super Contests in DPPt
>The Battle Tower has MUCH better AI than Platinum's Battle Frontier facilities, plus there's a Master Class now, where you can battle all the Gym Leaders, E4, Galactic Boss and Admins, etc
>Vastly improved Gym Leader rematches and Pokemon League rematches
>No HMs are required so you don't have to keep HM slaves in your party anymore
>Easy and convenient Bottle Caps and Mints
>Unlimited TMs
>Increased amount of Stickers Customization options compared to the originals
>Ramanas Park
>Pokemon following you
>Trainer Customization
>Etc.

I could go on, but I think you get the point. I think BDSP is a better game than Platinum and I think the only reason why a lot of people prefer Platinum is nostalgia, combined with the not very appealing graphics of BDSP. In other words, only graphic fags and nostalgia fags dislike BDSP.