The requirements for every game are different and the bottleneck might be somewhere else for every application, so there's no definite answer to your question.
That being said, I'm almost certain the graphics card won't be enough for recent games and probably is the bottleneck for most of them.
As an example, take a look at the StarCraft II System Requirements:
PC Recommended Specifications:
Windows Vista®/Windows® 7
Dual Core 2.4Ghz Processor
2 GB RAM
512 MB NVIDIA® GeForce® 8800 GTX or ATI Radeon® HD 3870 or better
OS? Check. CPU? Check. (almost) RAM? Check.
Graphics card? Not even close! According to PassMark Software - Video Card Benchmark Charts - Video Card Model List (always take that information with a grain of salt), the 3870 has a G3D rating of 718
, while the 4550 has a rating of 318
.