I read the manga a long time ago and was absolutely thrilled...
... until L dies, then I was done with it. I did finish it, but without much enthusiasm.
I had a lot of hope for the series and it had a lot of potential to resolve in a morally complex, heart-wrenching manner that would have made it all worthwhile. But I felt the later half of the series was just reduced to meaningless games that lacked any real depth. Maybe I was just expecting too much
I've only seen the anime, but I was disappointed when L died much earlier than I'd expected. The interactions and mental battles between Light and L were by far the most compelling parts of the show, and after it ended it seemed like the writers were (unsuccessfully) trying to replace that lost tension. They amped up the action (with Mello) and introduced a bunch of mediocre subplots with a boring central arc instead of one well-developed arc with just a few subplots like in the first 2/3rds of the series. (Though I did like Mikami and his backstory, so that makes it bearable for me.)
I was impressed with the English VAs, with the exception of the one who played Misa.
“If you hate a person, you hate something in him that is part of yourself. What isn't part of ourselves doesn't disturb us.” - Hermann Hesse