1) L2 cache
2) L3 cache
3) Clock speed
4) Front side bus
There's a lot more to it than that, A LOT.
The only way to really judge a CPU is to look at benchmarks. The Pentium 4 comes to mind when people erroneously judge a CPU based solely on specs.
The Pentium 4 clocked much higher and had much more cache (2-3X as much) as the competing Athlon 64 yet it was wasted by the Athlon just about every time. The Athlon simply had a more efficient design that didn't have an easily marketable tech spec that could measure it.