It thoroughly depends on what you want.
The downfalls I see about PBR is:
-It doesn't have any minigames like the past Stadium games
-It doesn't have an RPG mode like the previous 3D RPG ones (Colossuem and Gale of Darkness)
-The Pokemon just recycle their sprite SFX when sent out and such (like in the handheld games)
-Rotom, Giratina, and Shaymin's new forms aren't displayed. (as PBR is 2007, Platinum is of 2009)
What the upsides about it are:
-Your Pokemon are all 3D rendered and the graphics are amazing
-It's Wifi compatible
-You can get a special Pikachu with Surf after completing the game once
-It's compatible with all the Gen IV games (Diamond/Pearl, Platinum, HeartGold/SoulSilver)
-You can also get the Evolution items, like Dawn, Dusk, and Shiny stones, which you only get 2 in the games originally, to evolve Kirlia/Snorunt, Misdreavus/Murkrow, and Togetic/Roselia respectively.
It's a matter of what you want to enjoy from the game.
Personally, I have and enjoy the game. It's very challenging, and most hardcore fans/trainers like challenges.
I would prefer you to see if any of your friends (if you have any) have the game first, and give it a test run for yourself.
But, honestly, I wouldn't get it if you get bored easily.