THE GOOD: Counterstrike getting a Source makeover is akin to trading in Drew Barrymore for Charlize Theron. CS:S looks phenomal compared to the old CS. Environmental effects are given a huge boost in realism which you can see in the billowing clouds of dust, the mesmerizingly realistic water, and newly implemented physics engine. Nearly all the weapons have a satisfying, realistic feel to them and seem to be reasonably well balanced out between both the terrorists and the counterterrorists. Valve included some very skilled bots to practice and play against offline. The maps included are loaded with all the small details that you'd expect from a professional group of artists like Valve.
THE BAD: While Valve is working hard to add content to CS:S at the moment it suffers from a lack of maps and character models(only two, one T, one CT). Some people have complained about the hit boxes - unloading an entire clip at point blank into the face of your enemy and nothing. I usually attribute those instances to my own poor skills and shaky hand/eye coordination though.
OVERALL: I enjoyed this update to CS very much and can't wait for additional maps and character models from Valve.