it's free and it has:
-Ageia PhysX
- a really greate editor (well lightmaps are generated only for terrain but u can still import levels with lightmaps in static levels if u use external lightmapper, could be something like blender or giles etc.)
- shaders (a must have in 2009)
- supports opengl and directx, so its good for both customers area of the big graphics device competitors
- it runs on older hardware as well
- web deployment ( to play the games u only need a 3mb plugin and I already testet it with firefox and IE and everything worked fine, think for the typical indie casualgames it's really a great option)
- with it you can publish for win and mac os ( but for iphone and wii you must purchase other versions...but it gives u this support lol)
- multiplayer options and other www functions
- nice integrated animation editor
- stream audio and textures assets while game runs

I think it's a big option its free this makes the decision really easy, multiplatform is important too for publishers. If someone would make a good game with the free edition ( and u can make a good game, u can code in c# 1.1 javascript and boo and I think c# 1.1 is still good for these things there are even software developer who create their software with it), there would grow up the possibility that a publisher would buy for you or give the money for the pro license too fullfill your game with the features of pro if needed. for a hobbyist developer a good nearly complete package lol

some of the missed features in free version are not even in pro edition of others engine so I become happy with it even without those features. and imho I think it's just a question of time until they make an sdk aviable maybe for purchase or in a similar way like conitec did with open source license until you purchase the sdk license. ( and i mean sdk not the source code of the engine itself)