Differences Between Chaos Space Marines and Space Marines

The Chaos Space Marines have the same origins as the Space Marines, so have the same physical power. Due to their allegiance to Chaos, veteran Chaos Marines can be mutated, making them physically stronger, faster or otherwise superior. Chaos Marines are also virtually immortal, which allows them to learn advanced battlefield skills and tactics that Space Marines may not know.
They are equipped with power armour and weapons they had when they initially betrayed the Imperium, which are broadly the same as those used by Space Marines (although differences now exist with jump packs etc). The current setting of the Warhammer 40,000 game is about 10,000 years after the Horus Heresy, and, while the Imperium has made little technological advancement, Chaos Marines have far more limited access to the handful of new inventions that have appeared on the galactic scene. In general, anything developed since the Heresy is unavailable to them unless it has been captured; for example, Iron Warriors are known for capturing and using Imperial tanks. While Chaos Space Marines have only older technology, they compensate for this by having access to daemons and daemonic technology.