Nvidia has been pushing its proprietary PhysX technology for what seems like forever. The list of supported games remains relatively thin, with only a handful of recent titles taking advantage of the physics API. The most recent among those is Hawken, a free-to-play shooter that looks a lot like a Mechwarrior deathmatch. Nvidia has posted a video highlighting the game's PhysX effects, and some of them look pretty slick.
The turbulence-driven particle effects definitely improve the visuals in certain parts of the game, and I really dig the flurry of sparks produced when mechs are destroyed. However, using the same basic effect on the health power-up makes about as much sense as applying extreme tessellation to simple concrete barriers in Crysis 2. Both games are part of Nvidia's The Way it's Meant to be Played program, so we shouldn't be surprised.
In addition to showering Hawken with multi-colored particles, PhysX adds quite a lot of debris. That particular feature doesn't appear to have been over-used, and it certainly fits well within the context of the game. Who doesn't want to see more mechanical gibs?
These PhysX effects are effectively exclusive to Nvidia cards; you can enable them on a Radeon-based system, but the CPU will have to do all the heavy lifting. That's a shame, since AMD's latest graphics cards should have sufficient horsepower to produce similar eye candy themselves. Gamers would be better off if AMD, Nvidia, and developers could all agree on a common API. At least then, physics effects could impact the gameplay instead of being restricted to cosmetic flourishes. If you want to check out Hawken first-hand, you can grab the game here.