The only parts that really need to be replaced are the pedals. Apart from that everything works perfectly, especially the suspension is very good for the price, super plush and very well made. I was a bit sceptical about the brakes though, but they work surprisingly well and are powerful.
The 2010 model only had 175mm, this year they fortunately stepped it up. I'm a total beginner when it comes to downhill, but the first thing I did with it was some VERY technical dh, lots of roots and big rocks. The bike felt very nimble and quite agile, every single part worked great, no flat tires, no untrue rims afterwards, no noticeable bottoming out. If your intention should be only to ride dh with it, you should replace the fork with a dual crown though. The Vengeance is a high quality fork but it just doesn't have enough travel for extensive dh racing
cheers