Yes,it's a substantial improvement.
Here are some benchies (no games though and I couldn't match the exact processors in it (had to use a slightly slower Athlon II X2 265 and a faster Athlon X2 4600+ http://www.anandtech.com/bench/Product/190?vs=35
I would be looking for at least a triple core, preferably quad core CPU for games now. they are only a few more dollars. Dual cores wont give you smooth game play with many recent release games.