There are definitely some OTT elements in the cartoon, but in the end it's a personal favorite of mine. I watched before EpIII came out, and it filled in many gaps, i.e.

1. How did Anakin get those scars?

2. So what's the Clone Wars all about? (granted you learn this when you watch ROTS, but the cartoon nicely set up the main idea: jedi generals lead armies of clones against droids on many different planets)

3. We see Anakin knighted.

4. C3PO's armor change is mentioned.

5. Qui-Gon Jinn is not forgotten (he's in it! And Anakin is angry about his death)

6. Obi-Wandoes awesome things.

7. Anakin's a good pilot.

8. Mace Windu (and many other jedi) don't do nothing.

9. There are some actually funny moments.

10. We see the battle on Coruscant and Palpatine get captured.

11. We see Anakin add to his robotic arm.

12. We see Anakin and Obi-Wan board their fighters to go get Palpatine (leads right up to ROTS).

13. And, most importantly, we get to see Anakin and Obi-Wan be friends.

The only problem with the series is that Grievous is portrayed as a total bad ass - and he's not.