This game is truly the best SSS on this platform. I say it as: Capcom's finest hour for Megaman (aside from Megaman 2)
Well, let this talk for itself.
+Great bosses.
+Perfect for speed runs.
+Hard enough.
+Excellent sprites.
+Best backgrounds in the series.
+Good sound FX
+Perfect soundtrack
+Fun to play over and over again.
+X and Zero BOTH look like badasses.
+Bit and Byte rock.
- Vile sucks in this game
Overall: 9.2/10
Best entry in series, and that is a damn impressive feat.
Tip: Sigma's second form weakness = skull.
Tip 2: Hidden boss: Kill vile with the ray splasher. If you want Zero's shiny blade, before you get to the first door in Doppler Stage 2 once you kill Vile, switch to Zero, and kill the mini-boss.
Also, Kill Bit with Ice Lance, Byte with Tornado Fang.