Death Note...it's a question of how good the adaptation is.

Death Note is a series that has a lot of potential, a great reputation, really excellent writing...but didn't know when to end.

I can say with absolute certainty that the first three or four large arcs (depending on how you want to break up the series) are some of the most well written and intelligent parts of anime I've seen. Unfortunately, the series peaks relatively early, almost immediately after these arcs, and begins to lose focus. I'm intentionally being vague so you can enjoy it. The ending receives a lot of mixed reactions from viewers/readers.

I highly recommend watching (or even reading) the series up through those parts. It's right up to the end of episode 25. After that...the series fell flat for me.